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Glossary of Botanical Terms
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

go to top     A

A - Latin prefix: not, negative, without, lacking

Abaxial - facing away from the main axis e.g. lower surface of a leaf.

Abiotic - of non-living environmental factors (precipitation, temperature, wind) that affect living members of an ecosystem.

Abortive - development arrested while incomplete or imperfect.

Abscise - to cut off. Hence abscission, the normal separation of a leaf, fruit, or flower from a plant.

Abscisic acid - a plant hormone that induces abscission of leaves, dormancy and other adaptations to poor growing conditions.

Acanthocarpa - bearing spiny fruit. Also echinocarpa.

Acanthodes - (Greek: acantha = thorn) full of thorns or spines.

Acaulescent - without a visible stem.

Accrescent - continuing to increase in size after maturity or flowering, especially of floral parts.

Accumbent - of a pair of cotyledons curving back towards the hypocotyl so that their edges are turned towards the hypocotyl.

Achene - a small, dry, indehiscent fruit developing from a simple ovary with the seed distinct from the pericarp (fruit wall) which is generally attached to the seed at a single point. A naked seed.

Acicular - needle shaped, applied to an elongated tapering structure with a circular of eliptical cross section.

Aciform - acicular

Acre - A measure of land area equal to 43,560 square feet, 4,840 square yards or 160 square rods (Metric: 4,046.87 square meters). One square mile equals 640 acres.

Actinomorphic - of flowers that can be divided into symmetrical halves by cutting across any diameter.

Aculeate - armed with prickles.

Acuminate - with a long pointed structure formed by abrupt narrowing at an apex.

Acute - ending in a sharp point, forming an angle of less than 90 degrees.

Acutifolia - with pointed leaves.

Adaptive radiation - the diversification of a species under different, local environmental pressures to which it becomes adapted, eventually leading to the emergence of new species.

Adaxial - nearest to or facing towards the main axis e.g. upper surface of a leaf.

Adhesion - of two dissmiilar parts touching each other but easily separated and not fused or grown together.

Adnate - of unlike parts growing closely together, attached or fused.

Adpressed - lying close to another organ, but not fused to it.

Adventitious - arising in an irregular or unusual position such as roots arising other than from the radicle or primary root system; adventitious buds forming along a stem, generally in response to an injury.Not in the usual place.

Aenea (-us, -um) - bronze coloured.

Aerial - occurring above ground or water.

Aerial root - arising above ground, often from an axil. Provides a means for the plant to absorb moisture from the air.

Aeruginosa (-us, -um) - deep green with blue colour.

Aestivation - (estivation) - spending the summer months in a dormant state.

aff. - abbreviation of affinis = "close to", "similar to", "related to", as a descriptor of unresolved taxa.

Aggregata - clustered.

Agriculture - the science of farming plants and raising animals.

Alar -
i. wing-shaped, wing-like.
ii. in the fork or axil.
iii. cells in basal angles of the leaf.
iv. growth regulating chemical sprayed on fruit trees.

Alate - with wings or wing-like appendages.

Alatus (-a, -um) - with wings or wing-like appendages.

Alba - white.

Albiflora - with white flowers.

Albo - white - as a prefix in a compound word.
Hence:
    Albo-aurea - white and gold.
    Albo-marginata - with white edges or margins.
    Albo-maculata - with white spots.
    Albo-striata - with white stripes or striations.
    Albo-vittata - with lengthwise white stripes.

Algae - simple plants in the Division Protista, consisting of single cells to multicellular organisms, arranged in colonies or as filaments, and containing photosynthetic pigments. Many common algae are green because their cells contain chlorophyll.

Alkaloid - complex cyclic organic plant secondary metabolites, usually containing nitrogen in a cyclic ring, with a bitter taste and marked physiological activity on animals. Many of the 7000 known alkaloids are basic (alkaline). Many succulent plants contain alkaloids whose function may be to protect the plant from non-adapted herbivores, either by virtue of their unpleasant bitter taste or their toxicity. Examples include atropine, berberine, bryonine, caffeine, cocaine, colchicine, curare, lycorine, mescaline, mesembrine, morphine, nicotine, piperine, pyrrolizidine, quinine, strychnine, vincristine. Some of these alkaloids are used medicinally.

Alpina - i. from an alpine habitat. ii. of a dwarf growth habit.

Alpine - occurring above the tree line on very high and cold mountains.

Alternate - of leaves or other parts, not opposite or whorled, but placed singly at different heights on the stem.

Alveolate - of a surface or structure shaped like a honeycomb e.g. pollen or seed surface.

Amethystina - violet.

Amphibious - able to grow in both water and on land or growing with part of the plant in water or mud and part in the air.

Anastomose - to join together e.g. veins.

Anemophilous - wind pollinated.

Angiosperm - (meaning covered seed) - a flowering plant with ovules (seeds) enclosed in an ovary (fruit). Angiosperms developed about 100 million years ago (late Jurassic) and have become the dominant type of terrestrial plant, represented by at least 250,000 species, including both monocotyledons (e.g. Agave) and dicotyledons (e.g. Cactaceae).

Angustata - with a narrow stem.

Angustifolia - with narrow leaves.

Annatto - ( E160b ) A water and alcohol-soluble yellow-red dye made from the pulp surrounding the seeds in pods of the tropical American achiote tree Bixa orellana. Annatto is used as a natural food colouring (confectionary, cheese, margarine, smoked fish, custard powder, Caribbean cuisine) and as a fabric or leather dye. South American tribes used the brick-red triangular seeds for body paint and lipstick.
Structure of annatto

Annual - A plant that naturally completes its life cycle, from seed to seed, in one year.

Annual Rings - layers of wood laid down each year by the vascular cambium of woody plants, typically in trees. During the season of active growth in the vascular cambium, xylem cells are being added to the circumference of the xylem tissue. At the start of the growing season the cells grow fast and are large, but as the season progresses towards the dormant period fewer smaller cells are produced and growth eventually stops as the plant becomes dormant. The difference in size of the xylem cells laid down at the start and later in the growing season forms a line within the wood marking the boundary of an annual ring. The size of the xylem cells is also affected by the growing conditions. Hence changes in the width of annual rings can indicate changes in the climate.

Annular - ring-like.

Annulate - ringed or banded.

Anther - the male part of a flower producing pollen, usually on a filament. Anther and filament together are described as a stamen.

Antheridium - Pl. antheridia- the structure on the pteridophyte (fern) prothallus that produces the mobile male gametes.

Anthesis - the action of opening a flower or period of time during which a flower is open.

Anthocyanin - pink, purple, violet or blue water-soluble pigments colouring leaves, flowers and other parts. These pigments are sensitive to acidity or alkalinity (pH) turning red in acid and blue in alkali. Anthocyanins and betalains never occur in the same plant.
Structure of anthocyanin.

Antibiotic - a substance that destroys or inhibits the growth of bacteria and other microorganisms.

Apex - the top part of a plant or structure, the growing point.

Apical - located at the tip or highest point.

Apical dominance - inhibition of lateral bud development along a shoot by the terminal bud or growing point.

Apical meristem - the un-differentiated tissue at the tip of a shoot or root, that by division produces the precursors of the differentiated tissues, including vegetative, reproductive or floral organs.

Apophysis - an offshoot or projecting part.

Apothecium - a cup-shaped fruiting body produced by some lichens and fungi.

Appressed - turned upwards and lying closely, flat against something e.g. spines of some cacti.

Aquatic - growing in water.

Aquifer - a geological formation of permeable material that can store, transmit and supply water to a well or spring.

Arachnoid - cobweb-like, with soft entangled hair.

Arborescent - tree-like in size and growth habit.

Archegonium - Pl. archegonia- the structure on the pteridophyte (fern) prothallus that produces the sessile female gametes.

Areole - a modified side-shoot growing in the leaf axil, typically as a felted or multi-spined cushion, unique to the Cactaceae. From this point, spines, flower buds, stems, roots or offsets may arise. In most species, the areole is located on the tubercles or ribs. The areole is constructed so that breaking spines off the plant does not injure the underlying tissue.

Argentatus (-a -um) - silvered.

Argenteo - silver - as part of a compound word.

Argenteus (-a -um) - silvery.

Argentinus (-a -um) - from Argentina.

Aril - an outer covering, or sometimes merely an appendage, of a seed formed from the funicle. May be hard, waxy or pulpy.

Arista - an awn or bristle.

Aristate - with an awn or bristle.

Aromatic - with a resinous, spicy or distinctive smell.

Articulate - jointed or with points of apparent separation, usually marked by a swelling, line or sudden change in colour. Hence: Articulata - with joints.

Ascending - growing upwards.

Asclepius - ( Latin: Aesculapius) - the ancient Greek mythical god of healing from whom the name of the family Asclepiadaceae is derived. The Asclepiadaceae have recently been subsumed under Apocynaceae. More about Asclepius

Ascomycete - a large group of fungi including yeasts, milldews and truffles, with hyphae divided by septa and producing spores sexually within a typically cylindrical membrane forming a spore case or sac (ascus).

Asexual - without the involvement of fertilisation, propagation by division or the production of bulbils, offsets or stolons.

Aspera - rough to the touch.

Astringent - with a soapy or medicinal aroma because of the presence of saponium or other chemicals

Atropine - a poisonous, bitter alkaloid extracted from members of the plant family Solanaceae such as Atropa belladonna (deadly nightshade), Datura stramonium (Jimson weed), Hyoscyamus niger (Henbane) and Mandragora officinarum (mandrake). Atropine dilates the pupils, increases heart rate, and reduces salivation and other secretions by inhibiting binding of acetylcholine to acetylcholine receptors. It is useful medicinally, including as a cardiac stimulant and a treatment for organophosphate poisoning. Cleopatra is said to have used an extract from Henbane to dilate the pupils of her eyes.
Structure of atropine.

Atropurpurea - deep magenta.

Attenuate - gradually narrowed or tapered.

Aurantica (-is, -um) - orange.

Aurea (-a, -um) - golden.

Auriculate - ear-shaped.

Autotrophic - nutritionally independent of other organisms.

Auxin - a group of plant hormones such as indole acetic acid, produced by the tips of growing shoots in plants, that regulate the amount, type, and direction of plant growth by stimulating elongation of cells rather than cell division. Auxins diffusing down the stem away from the growing point produce concentration gradients that are responsible for apical dominance and phototropism. At the correct concentrations, auxins induces growth and fruit production even if the plant hasn't been pollinated (e.g. seedless watermelon). Commercially, auxins are used to promote root growth from cuttings, to promote uniform flowering, and to set fruit and prevent premature fruit drop.

Synthetic auxins such as 2,4-D and 2,4,5-T stimulate uncontrolled DNA and protein synthesis and are effective herbicides. 2,4-D is still used as a herbicide but use of 2,4,5-T has been banned because it tends to be contaminated with carcinogenic dioxin. Broad-leaved weeds like dandelions are much more susceptible to auxins than narrow-leaved plants like grass and cereal crops. At extremely low concentrations, 2,4-D is used to promote growth of orchid seedlings.

Auxotrophic - nutritionally independent of organic nutrients.

Axil - the upper notch or angle between the axis and any organ such as a leaf. Hence, "axilliary bud" is a bud in the leaf axil.

Axial System - the vascular elements running vertically up and down a stem, in contrast to the lateral system running horizontally or out to the margin of the stem. The axial system carries water and minerals up the stem in the xylem and carries glucose up and down the stem in the phloem.

Azureum - light blue.

go to top     B

Baccate - like a berry.

Bacciferous - bearing berries.

Bale - a standard bundle of agricultural merchandise such as straw, cotton or paper usually pressed or bound. The volume and weight of a bale depends on the commodity and locality.

Barbate - bearded or bearing tufts of long, weak hairs.

Barbed - bearing sharp, spine-like hooks which are bent backwards.

Bark - the protective exterior covering of the roots, stems and branches of woody plants, exterior to the cambium and including an inner layer of secondary phloem.

Barleycorn - a traditional English unit of length equal to one third of an inch. Use of seeds as average units of weight or length was common in societies based on agriculture. In the Anglo-Saxon era, barley was an important subsistence crop and barleycorns were used as units of length. Three barleycorns 'smooth and round laid end to end' were equal to the Saxon ynce (inch). Barleycorns, or grains, became the basis of all English weight systems.

Barren - sterile or otherwise incapable of reproducing.

Basal - at or referring to the base of any structure.

Basidiomycete - fungi including mushrooms, puffballs, rusts and smuts with hyphae divided by septa and that produce spores on a specialized club shaped cellular structure (basidium).

Basilaris - arising from the base.

Berry - a pulpy or fleshy fruit with one or numerous seeds embedded in the pulp.

Betaine - trimethylglycine - a quaternary ammonium compound with a sweet flavour found in sugar beet Beta vulgaris. Used for the treatment of muscular degeneration and metabolic disorders.

Betalain - a nitrogen-containing pigment characteristic of the family group Caryophyllales (Centrospermae) which includes the Cactaceae. Betalains are grouped as betacyanines (red-violet colour) and betaxanthins (yellow colour) and responsible for the red or violet colouration of some cacti under environmental stress. Betalain pigments are also found in some higher fungi. Betalains and anthocyanins never occur in the same plant.
Structure of betacyanine

Bi - two or twice, as a prefix.

Bicolor - with two different colours.

Biennial - a plant that typically lives two years from sowing, usually flowering in the second year.

Bifurcate - split in two.

Bilabiate - with two lips.

Bilateral - with equal sides eg bilaterally symmetric.

Binomial name - is used to describe each species according to the system devised by Linnaeus. The name consists of the capitalised name of the genus followed by the name of the individual species e.g. Euphorbia obesa

Biopesticide - a pesticide comprising a biological control control agent,which is usually pathogenic to the target species. An example of a commerically produced biopesticide is the bacterium Bacillus thuringiensis that kills only insects and not other animals. Its wide host range allows it to be marketed as a sprayable control for a variety of insects, but it may also kill unrelated desirable insects.

Bisaccate - having two little bags, sacs or pouches.

Blade - the expanded portion of a leaf or petal.

Bombycinus - silky.

Bostryx - a branching stem in which the daughter axes are all on one side. e.g. a raceme in which the flower stalks (pedicels) are all on one side.

Brackish - a mixture of salt and fresh water with intermediate salinity.

Bryonine - a yellowish-brown bitter alkaloid obtained from the root of White Bryony (Bryonia dioica). Extracts of the root have been used medicinally as an emetic and purgative but the toxicity of bryonine makes its use dangerous. However, it is still used in animal husbandry.

Bract - a reduced or modified leaf subtending an axis. Often found at the base of a flower or flower cluster and may form a cup around the flower in e.g. Compositae or may be brightly coloured and resemble petals in e.g. Poinsettia.

Branch - a natural division of a stem or trunk, especially a secondary stem growing off the main stem or trunk.

Bud - an unopened flower or a growing tip surrounded by its immature perianth segments or leaves.

Bud imprint - the outline of the margins, teeth or other features of one leaf impressed on another leaf while the two leaves are pressed together in the bud and remaining as a permanent marking after the leaves become separated. This effect is particularly marked in certain species of Agave.

Bulb - an underground food and water storage organ consisting of a short stem with one or more buds surrounded by modified leaves (scales).

Bulbil - a small vegetatively derived plant produced on an inflorescence.

Bush - or shrub - a low, often woody,plant normally branching from the base, rather than having a single stem that branches higher up. Also applied to a thicket or to an area covered with trees, bushes or scrubby vegetation in e.g. Australia or South Africa, or generally to any wilderness area.

Bushel - an English Imperial measure of volume, of a container or basket used to measure such a volume, typically used to measure dry goods such as grain or fruit. Such a cylindrical container would be 18.5 inches in diameter and 8 inches deep.A bushel = 4 pecks, 8 English gallons (defined as the Winchester bushel by King Edward 1 in 1303), 1.2844 cubic ft, 2219.36 cubic inches (Metric: 36.369 liters). A heaped bushel is traditionally 27.8 percent larger than a regular or struck bushel which has been leveled. Agricultural goods such as grain are traditionally sold by the bushel, but as they tend to settle during shipping disputes over volumes delivered can arise. Therefore bushels of a particular commodity are defined as standard weights, often enshrined in law and it is really the weight of goods that is sold rather than the volume.

go to top     C

Cactus - (Greek: kaktos = a prickly plant (Spanish artichoke) from Sicily) - A spiny, succulent, dicotyledonous plant of the family Cactaceae (Linnaeus 1737) native mainly to arid regions of North and South America, although some species are rainforest epiphytes. The fleshy stems and branches are characteristically furnished with tufts of hairs or spines coming from a common areole, a structure unique to this family. Only a few species of cacti have leaves. In the majority of species, photosynthesis is carried out on the green surface of enlarged stems that also serve as water storage organs.

Cactiform - with the growth habit of a dwarf cactus, having a ribbed or tuberculate green stem that is not much taller than wide.

Cactine - an alkaloid supposedly present in some Cactaceae such as Selenicereus grandiflorus but of doubtful reality. Cactine is said to have a digitalis-like action on the heart and to have diuretic properties.

Caducous - falling off early.

Caerulea (-is, -um) - blue.

Caespitose - forming a cluster or clump of stems by repeated branching of the stem above ground, at or near the base of the plant. Of plants that offset freely to form a large clump.

Caffeine - a methyl-xanthine alkaloid occurring naturally in some plants used to make beverages and foods including Coffea arabica berries (coffee), Thea sinensis leaves (Tea), Cola acuminata nuts (Coca Cola), Themobroma cacao beans (chocolate) and added to a wide range of manufactured foods. Caffeine is one of the most widely used mood-altering drugs and has probably been used through the whole of human history.

Calcarate - with a spur.

Calcicole - growing only in limestone soils

Calcareous - chalky, derived from limestone, or with an excess of lime.

Calcifuge - a plant unable to stand chalky (limy) soil.

Callus - a tissue composed of large thin-walled cells, usually produced in response to injury.

Calyptra - a hood or covering over the calyx or other part.

Calyx - a small whorl of modified leaves (sepals) at the base of a flower and, where present, enclosing the other parts of the flower in bud. These may occur individually or joined into a cup or tube and may be of any colour, but commonly green.

CAM metabolism - Crassulacean Acid Metabolism - a metabolic adaptation allowing temporary storage of carbon-dioxide as organic acids (e.g. malate) and later release of carbon-dioxide, by decarboxylation of these acids, for fixation into sugars. This allows uptake of carbon-dioxide during the cool nights, when water loss by transpiration is relatively low, while providing a store of carbon-dioxide for photosynthesis during the day. C-4 metabolism is typical of Agaves, Cactaceae, Crassulaceae. > Tropical grasses use a similar C4 pathway to support high rates of growth under optimum conditions.

Cambium - a layer of tissue giving rise to secondary growth in stems and roots by cell division. Seasonal growth within the cambium produces annual growth rings. The corky bark of the cork oak tree is formed from cambium cells.

Campanulate - bell shaped, applied to the shape of a flower.

Canadensis - from Canada, or sometimes more loosely applied to originating from the northeastern USA.

Canariensis (-e) - from the Canary Islands.

Candida - white.

Cane - a long woody pliable stem arising from the ground.

Canescence - a dense covering of very fine white or gray short hair.

Canopy - the foliage cover of a plant community especially woodland.

Caperatus (-a, -um) - wrinkled.

Capillaceus (-a, -um) - slender, hair-like.

Capillatus (-a, -um) - with hair.

Capitulum - pl. capitula -
i. a dense flat or globular cluster of sessile flowers or foliage e.g. inflorescence of clover, cauliflower, daisy and dandelion, head of lettuce.
ii. a dense fruiting spike of a cereal plant such as corn.
iii. the upper branches and foliage of a tree forming the crown
iv. any part forming a knob-like protruberance.

Capsule - a dry multi-chambered seed pod with many seeds per chamber that splits along several seams to open when dry and ripe.

Carbohydrate - a diverse group of large food storage molecules formed by linking sugar monomers into polysaccharide chains by glycosidic bonds.

Cardinalis (-a, -um) - red.

Carinate - keeled.

Carmine - a precipitate of cochineal (carminic acid) made by adding alum, cream of tartar, stannous chloride, or potassium hydrogen oxalate to a solution of cochineal. Sometimes proteinaceous substances such as egg white, fish glue or gelatine are added before precipitation. Carmine is used as a food dye, to colour alcoholic beverages, as a pigment in microbiology and in crimson ink.
Carmine lake - a pigment obtained by adding freshly precipitated alumina to a solution of cochineal (carminic acid).

Carotenoid - Carotene - a class of violet to orange or yellow fat-soluble unsaturated hydrocarbon pigments, usually with 9 conjugated double bonds, found in most higherplants and responsible for the colour of carrots, squashes and sweet potatoes. Carotene assists photosynthesis by transmitting energy from absorbed light to chlorophyll.
Dietary carotene is converted to Vitamin A in the liver of animals, which are unable to synthesise their own, and becomes concentrated in fat and cell membranes where it acts as an antioxidant. Carotene may cause a yellowish colour in people who consume large amounts in their diet. Carotene pigments extracted from plants are used to colour foods such as cheese and margarine.
The oxygenated derivatives of carotenes are known as xanthophylls.

Carpel - female reproductive part of flower including ovary, style and stigma, which may be solitary, grouped or fused.

Caruncle - an outgrowth on a plant or animal such as a fowl's wattle or a protuberance near the hilum of certain seeds.

Caryopsis - a dry, indehiscent seed-like fruit with a thin pericarp adnate to the seed coat, typical of cereal grasses e.g. wheat.

Cataphyll - a poorly developed leaf whose primary function is other than photosynthesis. e.g. cotyledon, scale leaf. In Cycads, cataphylls protect the apical meristem and are often produced prior to the emergence of leaves or cones.

Catkin - a cylindrical spike-like inflorescence consisting of a cluster of scaly bracts, often pendulous and unisexual.

Caudex - a swollen base to the stem and upper part of the root system used as a storage organ.

Caudiciform - of plants with a caudex.

Cell - the basic structual unit, which may be capable of replication or differentiation, from which all living tissues are made. Hence: Adj. cellular made from cells.

cell_wall - the rigid semi-solid layer surrounding a cell, protecting the interior from physical damage and resisting expansion from turgor pressure.Found in plants and many micro-organisms and constructed from a variety of materials:
Plant cell walls are constructed from a matrix of insoluble polysaccharides including cellulose, hemicellulose and pectin.
Algal cell walls contain cellulose and glycoproteins and a variety of other polysaccharides including alginic acid and sulphonated polysaccharides. Diatoms synthesise distinctive crystalline silicacell wallsfrom orthosilicic acid.
Fungal cell walls contain cellulose and chitin.
Bacterial cell walls, especially those of Gram Positive species contain peptidoglycan, a polymer of N-acetyl muramic acid and archebacteria contain pseudopeptidoglycan N-acetyltalosaminuronic acid.

Cellulose - the major constituent of plant cell walls and probably the most abundant organic substance on earth with about 1011 tons synthesised each year. Cellulose consists of beta-D-glucose units linked together with beta-1,4' linkages (compare with starch) into very long, high molecular weight polysaccharide molecules (typically up to several million kDa). Up to 50% of the carbon content of plants may be cellulose.

Central - positioned at or near the centre of an area, as opposed to being peripheral in position. A spine originating in the centre of an areole as opposed to those growing around the edge of the areole.

Cephalium - modified flowering zone of stems of certain species of cactus, often ornamented by copious development of hairs or bristles. In some species (e.g. Melocactus) stem growth ceases once the cephalium is produced. In others, a pseudocephalium is produced while stem growth continues.

Cereus - wax-like, candle-like.

Cereiform - with the growth habit of a cereus, having elongated, cylindrical and usually ribbed green stems.

Chamber - a hollow space. Hence: Chambered - with hollow spaces.

Character - a characteristic trait or feature sufficiently unique to be of value in distinguishing forms and defining relationships.

Charcoal - an amorphous form of carbon produced by partially burning or oxidizing wood or other vegetable material in fires from which air is partially excluded by covering with cut turf, or in large kilns in the absence of air. Uses include drawing material, as a fuel, filter, gas absorbent, etc.

Chartaceous - of or like paper or parchment. Usually not green.

Chartreuse - yellow-green.

Chasmathum (-a,-us) - with wide-open, gaping, flowers. Chemotropism - bending, growth or movement of a part under the influence of a concentration gradient of chemical substances. Aerotropism- special case of a response to oxygen.
See also: Tropism.

Chimera - the combination of tissues of different genetic origin in the same part of a plant. Examples of chimeras include some variegated cultivars of Sansevierias, although there can be many reasons for variegation.

Chinosol - 8-hydroxyquinoline sulphate, used as a fungicide and soil sterilant. This compound may inhibit seed germination and show some toxicity to seedlings.

Chitin - may be the second most abundant polysaccharide in nature, after cellulose to which it is structurally related, but see also lignin. At least 109 tons of chitin are thought to be synthesised each year. Chitin is found in the cell walls of many lowerplants such as yeast, mushrooms and other fungi. It also forms a substantial part of the exoskeleton shells of crustaceans, such as crabs shrimps and lobsters, as well as in the exoskeletons of marine zoo-plankton, including coepods, and in corals and jellyfish. Insects, such as butterflies and ladybird beetles, have chitin in their wings.
Chitin mainly consists of the amino-sugar N-acetyl-D-glucosamine linked together with beta-1,4' linkages, which may be partially deacetylated to a form of chitin called chitosan. Chitin is usually found complexed with other polysaccharides and proteins.

Chloranthus - with green flowers.

Chloro - (Greek: chloros = yellowish-green) green, as a prefix.

Chlorophyll - (Greek: chloros = yellowish-green) the green metallo-pigment in plants concerned with harvesting energy from light and transmitting the energy to an ordered chain of enzymes, ultimately responsible for the production of sugars. Each chlorophyll molecule contains a central magnesium atom chelated by four nitrogens from a large porphyrin ring and the two forms may be distinguished by substitution of a methyl group in chlorophyll a   for an aldehyde in chlorophyll b.   Structure of chlorophyll

Chloroplast - a specialised cytoplasmic organelle containing chlorophyll, characteristic of plants, and responsible for using energy captured from visible light to fix carbon from carbon-dioxide and synthesise carbohydrates as energy storage molecules. Like mitochondria, chloroplasts contain a small amount of DNA which encodes genes for a few chloroplast proteins.

Chlorosis - yellowing of plant tissue caused by many factors, often nutitional imbalance or poor illumination.

Cholla - any member of the genus Opuntia with short cylindrical-stems.

Chromoplast - a specialised cytoplasmic organelle containing pigments other than chlorophyll including yellow or orange carotenoid pigments.

Chromosome - tiny condensed X or Y-shaped sub-cellular bodies seen at the time of cell division, containing the genetic material (DNA) in the cell nucleus in association with packaging proteins such as histones. The number of chromosomes is usually constant for a particular species and species with different numbers of chromosomes may have difficulty hybridising.

Chrysantha (-us,-um) - golden.

Chrysocentrus - with a golden center.

Ciliate - fringed with very fine hair-like filaments.

Cincinnus - a branching stem in which the daughter axes are alternatively to the right and left. e.g. a raceme in which the flower stalks (pedicels) are alternatively to one side or the other.

Cinerea (-us,-um) - smoky gray, ashen gray.

Citrina - yellow.

Clade - A group of organisms with common ancestors, therefore sharing similar characteristics.

Cladistics - a method of classification of organisms based on their common ancestry and exploring their relationships within the branching evolutionary family tree or cladogram.

Cladogram - a graphical representations of the evolutionary divergence of species or related groups of species (clades) from common ancestors.

Cladophyll - Cladode - A leaf-like flattened photosynthetic stem or branch that resembles and functions as a leaf. Typical of epiphytic cacti e.g. Epiphyllum, Zygocactus

Class - a taxonomic group containing one or more Orders, ranking below Phylum or in botany, Division.

Clavate - club shaped. Elongated, with a gradual increase in diameter or increasing abruptly near the top.

Cleistogamous - of flowers that do not open, but nevertheless set seed by self-pollination.

Cloche - a glazed structure used to protect delicate plants from rain, wind and cold.

Clone - a plant which is genetically identical to its parent, produced vegetatively by offsetting, bulbils, cuttings or by in vitro propagation from meristem tissue.

Coalescent - growing together.

Coccineus (-a) - scarlet.

Cochineal - a red anthroquinone dye (carminic acid) made from a domesticated scale insect ( Dactylopius coccus ) and related species that live on prickly pear cacti (Opuntia species). Carminic acid is produced by the scale insect as an effective repellent for other insects such as ants. This dyestuff was used in pre-Hispanic Mexico for dying textiles. Although superceded by synthetic aniline dyes such as alizarin from the 1870's onwards, cochineal is still an important food colourant and used for dying textiles in folk art. Carmine is a precipitated form of cochineal.
Structure of carminic acid Cochineal bottle

Coelestina (-us, -um) - pale (sky) blue.

Colliculate - covered with small, rounded or hill-like elevations (colliculae) e.g. surface of seeds.

Coloratus - coloured, usually with a reddish tint.

Colpa - traditional Irish measure, originally a unit of livestock equal to one cow or horse or 6 sheep. Later adapted to specify a quantity of land which can support a horse or a cow for a year, approximately equal to an Irish acre of good land.

Colpus - an elongated aperture or groove with a length/breadth ratio > 2 in the wall of pollen grains. Hence: colpate = grooved.

Coma - a tuft of hair, usually terminal, especially on a seed tip. A tuft of leaves or bracts.

Commensal - literally "eating at the same table"- an organism that lives on or with another without harming it. See also parasite, symbiosis.

Compacta - compacted, compressed.

Complete - with all parts - of a flower with sepals, petals, stamens and pistils

Composite - a flower head composed of many small flowers, characteristic of Asteraceae.

Compost - decomposed vegetation, used to improve the soil in gardens.

Compound - with two or more like parts. Of leaves with several similar parts or lobes forming the whole. Of a flower head with outer ray florets forming "petals" surrounding the inner disc flowers, as in Asteraceae.

Compound leaves - leaves divided into two or more leaflets.

Compressa - flattened or pressed together.

Concolourous - coloured uniformly throughout, the same colour on both sides.

Conical - shaped like a cone.

Confluent - blending together or coalescing.

Connate - of similar parts growing from one base, joined or united to a single structure.

Connivent - coming close together or touching without joining.

Contact pesticide - a chemical that injures or kills insects which come into contact with it and does not have to be ingested to be harmful.

Copal - a resinous substance exuded from some species of tropical trees and hardening in air into a glassy solid ranging in colour from red to yellow or brown.

Cordate - heart-shaped, with the point away from the stem and the petiole at the broader, notched end.

Cork - (periderm) specifically the soft, low density bark of the cork oak tree, composed of cambium cells. Cork contains a natural wax, suberin, which protects the tree from water loss. The stems of many succulent plants harden and go brown with age and are often referred to as "corky".

Corm - a flattened fleshy underground stem, often acting as a dormant resting stage, capable of producing stems from the base and top and leaves and flower stems from the top.

Corolla - the collective group of petals which may occur separately or fused into a cup, tube or other structure.

Corona -
i. outgrowth of the perianth e.g. trumpet of a daffodil
ii. a ring of raised fleshy tissue on the corolla around but not adnate to the base of the stamens.

Cortex - a soft layer of tissue between the woody vascular tissue and epidermis, or external layer such as bark. Hence: Adj. Cortical.

Corymb - (Greek: korumbos = summit) a flat-topped or convex inflorescence with individual pedicels (flower stalks) branching from various points on the main stem. The outer or lower flowers open first, progressing from the margin inwards, and have the longest stalks so all flowers reach a similar height.

Cosmopolitan - distributed world-wide.

Cotyledon - 1. the first embryonic leaf or leaves in the seed. In some plants the cotyledons remain underground in the seedcoat.

Cotyledon - 2. a genus of succulent plants within the Family Crassulaceae.

Cotyledonosis - See: Krimpsiekte

Cotyledoside - a neuro-toxic bufadienolide cardiac glycoside: 7beta,8-epoxy-14-hydroxy-2alpha,3beta-(tetrahydro-3,5-dihydroxy-4-methoxy-6-methyl-2H-pyran-2,4-diyldioxy)-5alpha-bufa-20,22-dienolide
found in certain members of the Family Crassulaceae, especially in the genera Tylecodon and Cotyledon. Livestock ingesting plants containing Cotyledoside may develop a wasting disease, Cotyledonosis (Krimpsiekte)
See: Structure of cotyledoside  

Creation - most cultures subscribe to a legend that the earth or universe was created in a relatively short period of time by a supernatural power, together with all existing species (presumably including the Cactaceae and all other succulent plants.)
Compare with evolution.

Crenate - with rounded teeth or notched edges.

Crenulate - with shallow-toothed edges.

Crisped - with wavy, curled or crumpled margins.

Crispus (-um) - with wavy, curled or crumpled margins.

Cristate - crest-shaped or crested. An abnormal form of growth resulting from lateral distortion of the growing point.

Crown - the part of a tree above the first branching. The area from which new shoots arise or the point at which the roots meet the stem.

Cruciform - shaped like a cross.

Cryptogam - lower plants reproducing by spores rather than seeds, e.g. ferns, mosses, fungi etc.

Cucurbitacin - a toxic steroid developed by some plants, especially in the Family Cucurbitaceae as a defence against herbivores. Cucurbitacin is one of the most bitter tasting substances known. Some analogues have been shown to be toxic to cancer cells.
Structure of Curcurbitacin

Cultivar - a plant originated or selected artificially. Names of cultivars may be appended after the species name, (e.g. Lithops bromfieldii "Sulphurea") sometimes following the letters "cv."

Cultural requirements - the conditions which provide optimal growth of a plant in cultivation.

Cuneate - wedge-shaped with straight sides converging at the base.

Curare - a group of structurally related alkaloids that cause paralysis of the voluntary muscles by blocking acetylcholine receptors, when injected into the bloodstream and which are used as arrow poisons by South American tribal hunters. Curare is used medicinally as a muscle relaxant and as a treatment for tetanus.
d-tubocurarine - one of the most toxic alkaloids in the curare group, produced as a secondary metabolite in Chondrodendron tomentosum (Curare Vine), family Menispermaceae.
Structure of tubocurarine

Curcumin - a brightly-coloured yellow polyphenol pigment prepared from the root of turmeric (lili haldi), a member of the Zingiberaceae (Ginger Family). Several related compounds are present in turmeric at lower concentrations. Turmeric is widely used as a food colouring (E100) and is an important constituent of Indian food to which it imparts both flavour and colour. Curcumin is used in Indian Ayurvedic medicine and is said to have some activity against a wide range of medical conditions including arthritis, although little is absorbed from food. Curcumin has anti-oxidant and anti-inflammatory properties probably from inhibition of cyclooxygenases. In the presence of boric acid, Curcumin forms a red pigment (rosocyanine). This colour change is sufficiently sensitive and specific that it has been used as an analytical test for boron ions.
Structure of Curcumin

Curvospina - with curved spines.

Cuticle - a thin wax-like waterproof layer, composed of cutin, covering the epidermis. The outer coat of the seed.

Cutin - a waxy, water-impermeable complex fatty substance impregnating the cell walls and as a separate layer, the cuticle, on the outer surface of the epidermis.

cv. - abbreviation of "cultivar".

Cyathium - the cup-shaped inflorescence of a Euphorbia consisting of a cup-like involucre containing a single pistil (female flower) surrounded by male flowers, each contributing a single stamen. Variations on this occur with all-male or all-female flowers. The cyathium may be surounded by brightly coloured bracts that give the appearance of a large flower.

Cycasin - a toxic glycoside - methylazoxymethanol-ß-D-glucopyranoside - found only in Cycads.
  Structure of Cycasin

Cylindric - with a cylindrical shape.

Cyme - a flat-topped or domed inflorescence in which the central or terminal flower in the cluster opens first.

Cynarrhodium - a fleshy, hollow fruit enclosing achenes, typical of Roses.

Cytokinesis - the process of division of a whole cell, distinct from karyokinesis division of the cell nucleus.

Cytoplasm - the contents of the cell excluding the cell nucleus.

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Damping off - a potentially fatal fungal disease, usually of seedlings or cuttings.

Dasyacanthus - with dense spination.

Deciduous - shed periodically or annually or at maturity. Often applied to the seasonal shedding of leaves.

Decomposer - an organism (fungus, bacterium etc.) that breaks down and digests the remains of other organisms.

Decumbens - lying on the substrate with an ascending apex.

Decurrent - of a terminal spine extended down the leaf margin.

Decussate - of leaves arranged on a stem in opposite pairs at right angles to adjacent pairs of leaves above and below to form four vertical rows of leaves. Crossed or intersected in the form of an X.

Deflexed - curved or bent back down on itself or towards the plant surface.

Dehiscent - splitting or bursting open along defined lines e.g of a fruit.

Dehydrate - to lose a high proportion of water content.

Deliquescent - a tendency to absorb moisture and become liquid.

Dentate - with sharp teeth perpendicular to the margin.

Depressed - flattened from above.

Desert - a very dry area that receives less than 10 inches (25 cm) of precipitation each year.

Dessicated - dried, wrinkled.

Determinate -
i. of a growing tip terminated by a bud or flower which may stop or limit growth.
ii. of sequential flowering from a central or apical bud to lateral or basal buds.
See also: indeterminate

Dichotomous - forking equally, divided into two parts e.g. double-headed plants.

Dichotomous key - a systematic procedure for determining the identity of an organism (or other object) by making a series of binary choices, according to the characteristics of the object, each of which leads to other choices or to the correct name.

Dicotyledon - a large group of flowering plants with two cotyledons that initially emerge from the seed. The Cactaceae are dicotyledons.

Differentiation - the progressive physiological and morphological changes in cells, tissues, organs or the whole plant during development from meristem tissue to a mature or adult form. Differentiated tissues are usually more functionally specialised than undifferentiated ones.

Dimorphic - having two forms.

Dioecious - with male and female flowers on separate plants.

Diosgenin - a steroid sapogenin extracted from the tubers of Dioscorea (wild yam) species, especially D. mexicana and D. villosa. Diosgenin is used for the commercial synthesis of cortisone, pregnenolone, progesterone, and other steroid pharmaceuticals. Diosgenin also occurs in Fenugreek. Structure of Diosgenin

Diploid - having the basic two sets of chromosomes.

Disc flower -one of the multiple inner tubular florets on flower heads of Compositae (Sunflower family).

Dispersal - distribution, usually of seed.

Dissected - deeply divided or cut into parts.

Distal - towards the unattached or developing end of an organ.

Distichous - of opposite leaf pairs arranged along the stem in two ranks or planes, so each pair is parallel to those above and below. The result is a plant with a flat appearance.

Division - a major taxonomic grouping and primary division of a Kingdom, as in Kingdom Plantae, ranking above Class in size. See also: Phylum

DNA - deoxyribonucleic acid- the genetic material, contained in the chromosomes of all cellular organisms and some viruses e.g. potato spindle tuber virus. An extremely long double-helical linear polymer in which the gene sequences are encoded as the order in which four types of nucleotide bases occur, each paired with a complementary base. Groups of three base pairs in a structural gene specify the code for the 20 types of amino acids (and one or two rare ones such as selenocysteine) that make proteins.
Other sequences encode control functions such as start or stop (transcribing a sequence) signals. Much of the DNA in many organisms consists of apparently non-coding or repetitive sequences of unknown function.

Doctrine of Signatures - a theory dating back to Dioscorides (AD 40 - 90) that herbs resembling body parts are useful in treating ailments of that part. This philosophy was expanded by numerous writers including Coles, Galen, Paracelsus and Böhme. Böhme (1575 - 1624) suggested in "Signatura Rerum = The Signature of all Things" (1621) that God marked plants with a sign or signature so that by careful observation their purpose could be determined. This signature could also relate to the type of place in which such plants grow. The common names of many plants (hepatica, liverwort, lungwort, spleenwort etc.) originate in this belief.

Dormant - in a temporary state of suspended activity. Not in active growth, but protected (e.g. bud scales) from environmental stresses.

Dorsal - on or attached to the back of an organ.

Drip tip - a sharp elongated point on which atmospheric water accumulates from dews, mists and rain until the water drop is large enough to fall off the tip, to the ground around the roots of the plant. Drip tips are common on the leaves of tropical trees in areas of high rainfall and the spines of some Cactaceae also function in this way to scavenge moisture.

Drupe - a fleshy or pulpy indehiscent fruit with a thin outer skin, containing a single central hardened stone or pit containing a seed e.g. almond, cashew, cherry, date, elderberry, mango, olive, peach, plum. The hard, lignified stone originates as the ovary wall of the flower.

Druse - roughly spheroidal crystalline (e.g. calcium oxalate) or colloidal inclusions within tissues.

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Echinate - bearing prickles or spines.

Echinocarpa - with spiny fruit. Also acanthocarpa.

Ellipsoid - a compressed or flattened sphere.

Elliptic, Elliptical - oblong with regular flattened ends.

Emarginate - with notched ends or tips.

Embryo - the new plant developing from the fertilised egg cell (zygote) in the fertilised seed.

Endemic - originating from and confined to a specific, usually small, geographic area.

Endosperm - mass of nutrient tissue formed within the embryo sac.

Entire - with a continuous margin without teeth, lobes or indentations.

Ephemeral - a plant that completes its life-cycle in a very short time.

Epicalyx - a group of bracts below the calyx, resembling a (second) calyx.

Epicarp - the outermost layer of the pericarp of a fruit.

Epicotyl - the main axis of the seed embryo just above the cotyledons and continuing into the developing stem of the seedling.

Epidermis - the thin outermost protective cell layer, usually taken to include the waxy water-impermeable material (cuticle) overlying the living cells.

Epigeal - growing with one or more leaves above the ground. Germinating with cotyledons above the ground.

Epigenous - on or developing or growing on the upper surface of a part such as a leaf

Epiphyte - a plant (or other organism) that grows on another for support, without drawing any nutrients from it. Hence: Adj. Epiphytic.

Epithet - a descriptive adjective used as a noun forming part of the binomial botanical name of a species. e.g. gracilis = slender

Erectocentrus - with an erect central spine.

Erinaceae - with a hedgehog-like appearance.

Erose - ragged, with irregular random indentations.

Escape - an exotic species spreading from cultivation and becoming established in natural habitats.

Estuarine - associated with estuaries or river mouths, usually in brackish conditions.

Ethnobotany - the study of the uses of plants by various human cultures.

Etiolate - leaves and/or stems that are unnaturally long, often with a change of colour from the natural shade of green to yellow or white, due to insufficient light.

Euphorbus - physician to King Juba II (ca. 50 BC- 19 AD) of Mauretania. King Juba was said, by Pliny the Elder (23-79 AD), to have named a plant (probably Euphorbia resinifera) that he discovered on Mount Atlas in Morocco as "Euphorbea" after his physician. This is generally considered to be the origin of the name of the genus Euphorbia. A variety E. regis-jubae of Euphorbia obtusifolia commemorates King Juba himself.

Evaporation - the process of conversion of a liquid into a vapour or gaseous form. This change of state absorbs energy- the latent heat of vaporisation.

Evergreen - remaining green and leafy throughout the winter or resting season.

Evolution - a process of selection originally described by Charles Darwin in "The Origin of Species", whereby organisms possessing one or more characteristics conferring increased fitness, tend to survive and proliferate more successfully than similar organisms without these features. Natural selection therefore occurs for organisms possessing these desirable characteristics, and their numbers increase disproportionately within the population. Evolution generally proceeds very slowly, by selection for very small differences in characteristics. However, occasional introduction of large beneficial (in terms of fitness) changes into the gene pool leads to punctuated evolution where major changes occur over relatively short times compared with the geological record. The Cactaceae appear to be a group of plants which have diversified relatively recently, with few, if any, authentic fossils.
Compare with creation.

Excrescence - an outgrowth or protrusion from the surface.

Exine - the outer layer of the pollen grain wall largely composed of the polysaccharide sporopollenin and resistant to attack by chemicals.

Exotic - introduced from another climate, country or region.

Exserted - of stamens or pistils exceeding the length of the tepals.

Extinct - of a species which has completely died out. Species can also become "extinct in the wild" but persist in botanical or other collections.

Extinction - the process leading to complete loss of a species.

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F1 - of progeny derived from a first generation cross between distinct individuals.

F2 - of progeny from self fertile F1 hybrids.

Falcate - strongly curved or sickle-like.

Family - a taxonomic grouping of related genera with a similar floral pattern and other common characteristics, contained within an Order

Farina - a whitish mealy or flour-like covering. Hence: Adj. farinose, farinaceus.

Fasciation - malformation of a stem or other part usually with lateral flattening, cresting.

Fascicle - (Latin: fasciculus = small bundle) a small cluster or bundle of e.g. branches, flowers, leaves, or stems, or a bundle of vascular tissue. Of an inflorescence, a cluster of flowers in a leaf axil lacking an axis or cymose morphology. Hence: Adj. fasciculate: bundled or clustered.

Felt - a very thick layer of hairs or fibres.

Fertile - a plant with functional reproductive organs, producing pollen capable of fertilisation and seeds or spores capable of germination.

Fertiliser - a mix of essential nutrients supplied to plants to improve their growth or to correct a specific deficiency. For commercial fertilisers the proportions of Nitrogen:Phosphorous:Potassium are marked on the package as N:P:K ratios. More information.

Fibrous root - finely divided root system without obvious thickening or an enlarged central root.

Filament - stalk of a stamen supporting anther.

Flaccid - limp, flabby or drooping.

Flagellum - (Pl. flagella)- a whip-like hair, usually motile in lower plants and plankton. Hence: Adj. flagelliform = whip-like, flagellate = a single cell form of plankton with a flagellum.

Flavescens - becoming yellow.

Flavispina - with yellow spines.

Floccose - (of plants) having tufts of short soft woolly hairs.

Flora - all the plant species in an area. A book or treatise on plant species from a particular region.

Floral - relating to, or resembling, or made from, or containing flowers.

Floret - a small flower, especially as one component of a dense multiple flower cluster.

Flower - the complex reproductive organ of an angiosperm plant which may include sepals, petals, stamens and pistil. Flowers may include either male or female parts or both. The colourful parts of a flower and its perfume attract pollinators and guide them to the nectary, usually at the base of the flower tube. Pollination usually occurs incidentally to foraging for nectar or pollen as food. Xerophytic plants may have flowers that are produced and open in response to rain and produce seed within a few weeks of pollination, thus completing their life cycle. Species with tubular red flowers have often evolved to attract humming birds and other avian pollinators. Some night-flowering species have specialised to attract bats with foetid fleshy blooms or moths with large strongly-perfumed flowers.
See also: catkin, corymb, cyathium, cyme, fascicle, panicle, raceme, spadix, spike, thyrse umbel

Flower head - a dense arrangement of flowers arising from a common point as in e.g. Umbelliferae or Compositae.

Flowering plant - an angiosperm.

Foetid - with an offensive stinking odour.

Foliage - the leaves of plants.

Follicle - a dry dehiscent, many-seeded fruit derived from one carpel and splitting along one suture.

Forest - a plant community dominated by trees or other large plants e.g. large Aloes, Yuccas.

Form - the smallest degree of consistent differentiation between plants which may be formally named e.g. spine length or flower colour.

Fragilis - fragile, easily broken.

Fruit - the mature ripened reproductive body (ovary) of a seed plant which encloses the seed in fertile species of plant. True fruits develop from the ovary wall. See: pericarp. Many fungi, myxobacteria (slime moulds) and lichens produce a fruiting body, a macroscopic reproductive structure enclosing the spores. Fungal fruiting bodies often have distinctive sizes, shapes, and colours characteristic of each species.
See also: achene, apothecium, berry, capsule, caryopsis, cynarrhodium, drupe, follicle, pepo, pitahaya, pome, samara

Frutescens - shrubby.

Fulgida - glittering, shining.

Fulvous - yellow or tawny or yellow flecked with a mixture of grey or brown.

Fungus - (Pl. fungi)- simple spore-producing eukaryotic plants that obtain energy and nutrients by breaking down other organic material and abrorbing it through their cell walls. The Kingdom Fungi includes yeasts, moulds, mildews, mushrooms, rusts, slime moulds, smuts, and toadstools.

Funicle - the stalk of an ovule or seed. The thread like tissue connecting the developing seed, via the hilum, to the fruit. (Latin: funiculus = little rope)

Furlong - English unit of length equal to 660 feet, 220 yards, 40 poles, 10 chains or one-eighth of an English mile (Metric: 201.168 meters). Literally a 'furrow long' from Old English furlang, the length of a single furrow that a horse could plough without stopping and hence the length of a medieval field. Still used in horse racing.

Furrowed - with parallel longitudinal grooves or channels.

Fuscous - dusky, blackish or a greyish-brown colour.

Fused - joined and growing together.

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Galvanotropism - bending, growth or movement of a part under the influence of an electric current.
See also: Tropism.

Gamete - the male and female sexual cells that combine at fertilisation to form the zygote.

Gametophyte, Gametophore - the part of the plant which bears the gametes or sexual cells. The haploid state of life of a sexually reproducing plant.

Gamopetalous - (sympetalous), of a flower with the petals of the corolla more or less fused, to form a tube or funnel.

Gelatinous - a slimy and sticky jelly-like substance with a water base.

Geminate - arranged in pairs.

Gene - an inheritable factor, carried on the chromosomes, determining a character or trait in an organism.

Generic - pertaining to a genus.

Genetics - the study of inheritance of characteristics.

Genotype - the genetic characteristics of an organism.

Genus - (pl. Genera) a group of related species with sufficiently distinct unique characteristics in common to be treated as a separate unit. The name of the genus forms the first part of the binomial name of each species, and is always capitalised.

Geophyte - a perennial plant propagated by buds on underground bulbs, tubers, or corms that act as food storage organs and enable the plant to survive adverse conditions such as drought or Winter.

Geotropism - a growth response to gravitational forces causing bending, growth or movement of a part under the influence of a gravitational field.
See also: Tropism.

Germination - the sprouting of a seed. Development of a spore.

Gibberellin - a group of plant hormones based on gibberellic acid produced by seeds, mosses, ferns, algae and fungi. Gibberellins stimulate synthesis of nucleic acids and proteins and promote cell elongation, meristematic growth at the root and shoot tips, mobilisation of food reserves in seeds and other processes. Their absence results in the dwarfism of some plant varieties. These relatively expensive chemicals have been used commercially in the production of seedless grapes and navel oranges and in plant micropropagation from tissue culture and have been found to reverse the effects of some herbicides.Compare with auxins which inhibit root growth in high concentrations.

Gibbous - swollen on one side, usually near the base, to form a pouch or sack.

Glabrous - smooth, without hairs or protrusions.

Gland - a multi- cellular secretory structure producing oil, resin or other liquid, usually as a protruberance or appendage, but sometimes as part of a surface.

Glaucous - bluish grey or bluish green often as a result of a wax-like bloom.
Epithets: Glauca - Glaucum - denote plants with glaucous foliage.

Glaucescence - a fine bloom, blush or coating of whitish or bluish-white substances, usually microscopic particles of wax, easily rubbed off the surface.

Globose - spherical or spheroidal.

Glochids - spines or hairs, usually small, brittle and barbed. Occurring in tufts and characteristic of Opuntioideae.

Glycoprotein - a diverse group of proteins which are modified by addition of short chains of typically 8-10 sugar residues covalently linked to their polypeptide structure.

Gracilis - slender.

Graft - a shoot, bud or other tissue joined to, and growing on, another compatible plant.

Greenhouse effect - the trapping of heat from sunlight by atmospheric gases ( greenhouse gases ), including carbon dioxide, methane and water, which raises planetary temperatures above those expected from a simple model of heat radiation received from the sun and re-radiated into space. The high surface temperature on the planet Venus is caused by an extreme form of greenhouse effect.

Grey Water - effluent water suitable for use in gardens, from light domestic use for baths, showers, washing clothes or dishes and containing less nitrogen and less likely to be a disease vector than water from toilets.

Guard cell - one of two crescent-shaped cells which surround and control the opening and closing of the aperture of the stoma and thereby regulate passage of gases and water vapour through a plant's epidermis.

Gum - material resulting from the breakdown of plant cells including their carbohydrates. On exposure to air, gums dry and harden.

Gummifera - bearing gum.

Guttation - exudation of liquid water from plants.

Guttered - of leaf margins folded inward.

Gynoecium - the female part of the flower consisting collectively of the carpel(s) or pistil(s).

Gymnosperm - with naked or unprotected ovules (seeds) e.g. conifers, cone-bearing plants such as Welwitschia. Gymnosperms do not produce flowers, but instead release pollen through the air to the female ovule, causing fertilization.

Gynostegium - a crown of united stamens and style protecting the gynoecium and typical of milkweeds (Asclepias).

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Habit - the general form and growth pattern of a plant.

Habitat - the place in which a plant, or other organisms, naturally grows or lives.

Hair - a long thin epidermal appendage, either formed from a single elongated cell or consisting of a single row of cells.
See also: arachnoid, barbate, canescence, capillaceus, capillatus, ciliate, cephalium, coma, felt, glabrous, glochids, hirsute, lanate, lasiacantha, penicillate, pubescent, pubispina, scabrous, trichome, villous, woolly

Hairy - with a covering of hairs.

Half life - the time taken for the value of something to reduce to half of that value. Of a radioactive isotope, the time taken for half of the atoms to decay.

Halophyte - a plant adapted to, growing in and tolerating salty environments.

Haploid - having a single set of chromosomes.

Haptonastic - a movement response to a touch stimulus.

Hard Water - contains salts (usually calcium or magnesium) that interfere with formation of a lather from soap. Hard water used for irrigation of plants may leave white marks on foliage and the salts accumulate in the soil.

Hardwood - strong, dense wood from slow-growing broad leaved trees.

Hardy - of a plant able to survive the extremes of climate, often taken to mean resistance to cold and frost.

Haulm - the collective stems or tops of crop plants (e.g. beans, peas, potatoes, grains, grasses) after the crop has been gathered, as used for bedding or thatching. Occasionally applied to a single stem.

Haustaurium - (Pl. haustoria)- a specialised organ through which a parasitic plant absorbs nourishment from its host.

Heath - open land covered with low-growing shrubs such as heather.

Hectare - (ha) a metric unit of area equal to 100 Ares (2.471 acres) and equivalent to 10,000 square meters (107,639 square feet).

Hedge - Hedgerow - a border, fence or boundary formed by a row of closely planted shrubs or bushes often trimmed to a formal shape. The number of species forming a hedge tends to increase in proportion to its age.

Heel - a small portion of the previous year's growth at the base of a cutting.

Hemicellulose - heterogeneous mixture of polysaccharides resembling cellulose, but of lower molecular weight and less complex. Hemicellulose is insoluble in hot water or with chelating agents, but can be extracted with dilute aqueous alkali. Present in allmost all plant cell walls where hemicellulose binds with pectin to cellulose to form a network of crosslinked fibres, but found especially in woody tisues. Includes xylan, glucuronoxylan, arabinoxylan, arabinogalactan II, glucomannan, xyloglucan and galactomannan.

Herb - a vascular plant lacking a woody structure.

Herbaceous - dying to the ground periodically or lacking a definite woody structure.

Herbivore - an animal that eats only plants.

Hermaphrodite - with both male and female reproductive parts usually in the same flower.

Heteromorphus - with an irregular or unusual shape or structure.

Heterotroph - an organism that can not make its own food and consumes other organisms to survive.

Heterozygote - with unlike genes on any particular pair of chromosomes.

Hibernation - spending the winter months in a resting or dormant state.

Hilum - the small scar on a seed coat where it was attached to the seed pod by the funicle.

Hirsute - pubescent, with coarse, stiff hairs.

Holistic - of, concerned with, or dealing with whole or integrated systems rather than with their parts.

Holotype - the type specimen of a taxon as designated in the author's description.

Homology - having the same phylogenetic origin, but not necessarily identical form or function.

Homonym - a name that already exists for another plant. The newest name is illegitimate and must be changed.

Homoplasy - of different species with similar characters that have evolved separately and are not from a common phylogenetic origin.

Homozygote - with identical genes on any particular pair of chromosomes.

Hooked - with a straight basal portion and a tip curved into an arc.

Horticulture - the science of growing plants for decorative effect or for consumption as food.

Horizonthalonius - with a flat, level disc.

Hormone - a chemical substance produced in a plant tissue, capable of diffusing or transport to other parts where it's presence or gradients regulates specific functions such as abscission, differentiation, flowering, growth and tropisms.

Hort. - as part of a species name means "associated with gardens," "of garden or horticultural orgin". Usually applied to a selected form or cultivar or hybridised so that the true origin is obscure.

Host - the organism on or in which a parasite lives and from which it derives its nourishment. Sometimes also used for the plant on which an epiphyte lives.

Humus - the organic component of soil, composed of partially or completely decayed plant and animal remains that provides nutrients for plants and increases the ability of soil to retain water.

Hyaline - translucent.

Hybrid - progeny from an inter-specific (or inter-generic) fertilisation, often of intermediate appearance to the parents.

Hydathode - a specialised gland or pore on the surface or leaf margin of higher plants that exudes water from the plant tissues or in some cases can absorb water on the leaf surface.

Hydrotropism - bending, growth or movement of a part in response to a water source.
See also: Tropism.

Hypanthium - a cup-like, ring-like or tubular base of a flower carrying on its rim the calyx, sepals, petals, and stamens and often superior to the ovary.

Hypanthodium - an inflorescence composed of an aggregate of flowers on the inner fleshy wall of a concave capitulum e.g. Ficus or the characteristic flat "shield flowers" of Dorstenia.

Hyperplasia - an excessive multiplication of cells.

Hypocotyl - the main axis of the seed embryo just below the cotyledons and continuing into the developing primary root of the seedling.

Hypodermis - a layer of cells below the epidermis.

Hypogeal - happening, living or remaining below ground. Of the emergence of cotyledons below the surface of the ground or within the sead coat.

Hypogeous - below ground.

Hypostase - a basic substance, a group of specialised thick-walled cells between the ovule and the vascular bundle, a disk of woody, lignified tissue at the base of the ovule in some plant families.

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Idioblast - a special cell in a tissue which differs markedly in form, size or contents from other cells in the same tissue.

Imbricate - with overlapping edges.

Imperfect - flowers lacking either pistils or stamens.

Incumbent - resting or leaning upon. Also applied to a pair of cotyledons curving back down the hypocotyl so that the back of one is turned towards the hypocotyl and the back of the other is turned away from it.

Incurvispinus - with inwardly curved spines.

Indigenous - occurring naturally in an area. Not introduced.

Indehiscent - failing to split open at maturity.

Indeterminate -
i. capable of continuing to grow at an apex or tip.
ii. of sequential flowering from lateral or basal buds to the central or apical bud.
See also: determinate

Inermis - (Latin: unarmed) of a plant or plant part without spines of thorns.

Inferior - below another organ or part.

Inflorescence - a flower cluster, including bracts, on a stalk.
See also: catkin, corymb, cyathium, cyme, fascicle, panicle, raceme, spadix, spike, thyrse umbel

Inorganic - of molecules or chemistry based mainly on elements other than carbon.
See also: Organic.

Insectivorous - trapping and obtaining nutrients from insects.

Integument - the covering of an ovule or other structure.

Intergrading - merging from one form to another by a continuous series of intermediate forms rather than divided into discrete sets.

Internode - part of a stem between two nodes.

Intertextus - interwoven.

Introse - facing inwards.

Involucre - a whorl of small leaves close underneath a flower or flower cluster.

Irradiance - the amount of light energy illuminating the Earth per unit area.

Irregular flower - a flower in which similar parts are unequal in size, form or extent of fusion as in e.g. Leguminosae (pea family). Often bilaterally symmetrical.

Isotropic - having the same property in all directions.

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Joint - a pont where a side-shoot or leaf grows out of a stem. A single section or segment of a stem composed of a series of units.

Juvenile - young or immature, not having flowered.

Juvenile leaves - the first set of leaves, especially when differing from the mature leaves.

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Karyokinesis - the process of division of a cell nucleus, distinct from cytokinesis division of the whole cell.

Karyotype - the gross morphology of the chromosomes.

Kewensis - from the Royal Botanic Gardens, Kew. UK.

Kingdom - the highest grouping of similar organisms within the system of classification. Terrestrial life is divided into five Kingdoms: Animalia (animals), Plantae (plants), Fungi, Protista (protozoans and eucaryotic algae), and Monera (blue-green algae).

Krimpsiekte - Cotyledonosis - "shrinking disease" - a disease of livestock in Southern Africa, caused by consumption of plants from the genera Tylecodon and Cotyledon that contain bufadienolide cardiac glycosides such as Cotyledoside. These cumulative toxins cause symptoms of exercise intolerance, paresis, paralysis, torticollis, paralysis of the lower jaw and tongue, dysphagia, drooling of saliva, abdominal pain and convulsions followed by death within a few hours. Secondary poisoning occurs in humans and animals that eat contaminated meat from diseased animals. There are no significant lesions at autopsy.
Structure of bufadienolide Structure of cotyledoside

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Labium - a lip.

Lacteus - milky.

Lamella - a thin plate or layer.

Lamina - the blade or expanded part of a leaf.

Lanate - with long, soft wooly hairs.

Lanceolate - shaped like a long narrow lance with a gradual taper from the base to the tip.

Lasiacantha - with shaggy or hairy spines.

Lateral- growing or positioned at the sides.

Latex - a milky aqeous emulsion containing a variety of organic substances, often including rubber and various proteins. Commercially, latex produced from within bark of the rubber tree is coagulated by heat to produce natural rubber.

Laticifer - cells containing a characteristic milky fluid called latex.

Leaf - an outgrowth from a node on a plant's stem. Leaves come in many shapes and sizes, but are often flattened to maximise their surface area for capture of energy from sunlight (photosynthesis) using chlorophyll contained in chloroplasts, thin to allow light to penetrate the tissues and oriented to optimise exposure to sunlight. In most plants, leaves also allow gas exchange, guttation, respiration and transpiration to take place. Leaves can store food and water and may be modified for other purposes.
See also:
- leaf blade: simple, compound, palmate, peltate, pinnate, scabrous, trifoliate
- leaf arrangement on the stem: alternate, decussate, distichous, opposite, rosulate, spiral, whorled
- leaf margins: ciliate, crenate, crenolate, dentate, entire, guttered, serrate, sinuate, teeth
- leap tip: acuminate, drip tip, emarginate, hooked, lanceolate, mucro, mucronate, spatulate

Leaflet - part of a compound leaf.

Lectin - a diverse group of plant proteins capable of aglutinating cells (such as red blood cells). Lectins contain sites that recognise and bind to sugar residues, such as those included in the structure of glycoproteins. Ricin is a notorious toxic lectin from the seeds of the castor oil plant.

Lectotype - a specimen selected from the original type material to serve as the nomenclatural type when a holotype was not originally designated, or is missing.

Leggy - of plants exhibiting excessive, rank growth, often caused by excessive watering, application of fertiliser or insufficient light.

Legume - i. a fruit with a single compartment that splits along two sutures or seams e.g. pea pod.
ii. a plant in the family Leguminosae (peas, beans) that can fix nitrogen from the soil due to the presence of symbiotic bacteria (e.g. Rhizobium species,) in root nodules.

Lenticel - a pore in tree bark through which gas exchange occurs.

Lenticular - shaped like a biconvex lens.

Leptocaulis - with slender stems.

Liana - liane- a woody, climbing vine.

Lichen - a complex differentiated organism formed by a symbiotic relationship between an algae and a fungus.

Lignin - a diverse group of non-toxic organic polymers often associated with cellulose in the walls of many plant cells, especially in woody plants. In this form, lignin acts as a cement to exploit the strength of cellulose fibres, while allowing flexibility. The mechanical properties of this natural composite material (wood) compare favourably with many man-made composite materials such as fibre-glass. After cellulose, lignin may be the second most abundant biopolymer in the world with an estimated annual production of 108 tons, but see also chitin.
Lignin is formed by the irreversible removal of water from sugar monomers to create phenolic aromatic structures. Polymerisation and extensive cross-linking occur to create very large three-dimensional lignin molecules. Sometimes lignin is isolated as a brown powder, but more often as a gummy mixture of lignins with a wide range of molecular weights. Lignin resists attack by most microorganisms, and anaerobic processes tend not to attack the aromatic rings at all. Aerobic breakdown of lignin is slow and may take many days. Hence, the presence of lignin strongly affects the bio-degradeability of woody materials.
The presence of lignin is demonstrated by a characteristic red colour on contact with sodium hypochlorite (bleach).

Linear - long and narrow with parallel or nearly parallel sides.

Linnaeus - Carolus Linnaeus (1707-1778) - a Swedish scientist who devised the binomial nomenclature used to identify every living species. The Linnaean System of classification is based on a simple hierarchical structure in which all known organisms are listed according to Kingdom, Phylum, Class, Order, Family, Genus and Species.

Lithophyte - growing on rocks.

Littoral - growing on the beach.

Litteralis - belonging to the sea shore.

Lobe - partial rounded portion of a leaf or other organ, separated from the whole by a deep indentation that does not break the continuity of the structure.

Lobed flower - a tubular or funnel-shaped flower opening into petal-like segments.

Locule - individual compartment of an anther, ovary or fruit.

Loculicidal - longitudinally dehiscent along the capsule wall between the partitions of the locule so as to split it into two parts,as in the fruits of Liliaceae.

Lumen -
i. A pore or passage through a tubular structure.
ii. an internal cavity, space or void. e.g. cavity within the plant cell cell wall.
iii. the SI measurement of light output (or luminous flux) used to label light sources as a measure of total light output. 1 lumen (lm) = 0.00146 W.
A unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions.

Lumper - coloquial - one who takes a broad view of a genus, combining variant forms into individual species.

Lutescens - yellowish.

Lycorine - a toxic alkaloid found in Amaryllidaceae (daffodil family) all members of which should be regarded as poisonous. Poisoning by daffodil bulbs, confused with onions, is fairly common. Symptoms of ingestion include salivation, vomiting, diarrhea, collapse and death, depending on the dose. Lycorine inhibits protein synthesis and cell division and is of interest as an anti-tumour agent.
  Structure of Lycorine

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Macrocentra - with a large central spine.

Macromeris - with long or large divisions.

Macrorhiza - with long or large roots.

Macrozamin - a toxic glycoside - methylazoxymethanol-ß-primeveroside - found only in Cycads.
  Structure of Macrozamin

Macula - a spot or blotch. Hence Adj. maculate = with spots or blotches.

Maguey - the Agave or century plant, especially A. americana but includes several other species. Also applied to cordage and fabrics made from fibres of the Maguey plant.

MAM - a neurotoxin - methylazoxymethanol - found exclusively in Cycads as its glycosides as e.g. Cycasin, Macrozamin and related compounds. MAM is released from the glycosides by enzymatic processing in intestinal bacteria. Hence the glycosides are only toxic after ingestion.
  Structure of methylazoxymethanol

Mamilla - nipple-shaped tubercle with an areole at its tip.

Mamillate - with breast or nipple shaped projections.

Margin - the edge of a leaf or other organ.

Marginal - along the margin or edge.

Marine - of the sea or saline water.

Maritime - of the sea, coastal.

Marsh - a swampy waterlogged area, either fresh or saline.

Matrix - a medium in which something is embedded.

Mature - applied to cells and tissues that have differentiated into their final adult form assuming the function or form characteristic of cells or tissues found in a fully developed part of the plant.

Mayahuel - Aztec Goddess of Maguey ( Agave ), fertility, alcohol and pulque. Drawing of Mayahuel

Median - in the middle or axial plane.

Medulla - soft internal tissues such as pith.

Megasporangium - Pl. Megasporangia - a structure in spore-bearing plants such as Cycads in which female megaspores are formed, similar to the ovule in seed plants.

Meiacantha - with smaller or fewer spines.

Meiosis - a special type of cell division at the sexual stage of a life-cycle when the diploid or other normal chromosome number is halved in the production of haploid gametes.

Melanacanthus - with black spines.

Membrane - i. a thin pliable sheet of material that separates and forms the interface between two environments.
ii. a thin flexible sheet of tissue connecting, covering, lining, or separating various parts or organs.
iii. a thin (10 nm) structured bi-layer of phospholipid and protein molecules surrounding every biological cell and intracellular organelles such aschloroplasts, mitochondriaand the cell nucleus. Functionally distinct proteins floating in the membranes of cells and organelles control the passage of substances into and out of the enclosed space, catalyse chemical reactions at the membrane surface and allow cell-cell recognition.

Meristem - the growing tissue comprised of stem cells capable of repeated division and differentiation into permanent structures.

Mescal - a strong alcoholic liquor, similar to Tequilla, made by distillation of a fermented preparation of the starchy core of Agave angustifolia and other species. Also a common Mexican name for certain Agaves.

Mescaline - a halucinogenic alkaloid found in Lophophora williamsii and other species of cactus traditionally used in native American Indian religous ceremonies and medicine.
  Structure of Mescaline

Mesembrine - a narcotic alkaloid found in Sceletium tortuosum (kanna) and other species of Aizoaceae (Mesembryanthemaceae). Mesembrine inhibits serotonin uptake thus increasing extracellular levels of serotonin and therefore increasing serotonergic neurotransmission. Mesembrine is also an inhibitor of the enzyme phosphodiesterase. Mesembrine is certainly mood-altering and may be an anti-depressant.
  Structure of Mesembrine

Mesomorphic - adapted to conditions that are neither very wet nor especially dry.

Mesophyll - the photosynthetic layer of tissue of a green plant underneath the epidermis.

Microcarpa - with small fruits.

Micromeris - with small parts or divisions.

Micropyle - a small pore in a seed that allows water absorption. A minute opening in the wall of an ovule through which the pollen tube enters.

Microsperma - with small seeds.

Microsporangium - Pl. Microsporangia - a structure in spore-bearing plants e.g. Cycads in which the male microspores form, similar to the pollen sac in seed plants.

Midrib - the main or central rib of a leaf.

Mitosis - the normal process of cell division when the diploid or other normal chromosome number is conserved to produce two daughter cells with identical numbers of chromosomes to the parent cell.

Mitochondria - a functional organelle in the cell cytoplasm, of both plants and animals, containing highly ordered membrane-bound arrays of enzymes and proteins involved in respiration and energy metabolism. Mitochondria contain a small circular piece of DNA, which carries genes for a small number of mitochondrial proteins. Mitochondria are inherited almost exclusively from the female parent, and DNA sequences encoding mitochondrial genes are analysed to determine inter-specific relationships and the slow rates of mutation in mitochondrial DNA sequences are used as one form of "molecular clock."

Monocarpic - a plant that flowers only once in its life and then dies.

Monocotyledon - a large group of flowering plants with a single cotyledon that initially emerges from the seed. The Agavaceae and Liliaceae are monocotyledons.

Monoculture - growth of a single species in a particular area.

Monoecious - with both male and female reproductive organs on the same plant.

Monomorphic - with a single shape or form.

Monophyletic - of a group of organisms sharing and including a common ancestor, and including all the descendents of that common ancestor, therefore with similar characteristsics. Otherwise known as a clade.
See also: paraphyletic, polyphyletic.

Monotypic - a genus with a single representative species.

Monstrose - Monstrous - an abnormal uncoordinated form of vegetative growth, often with random production of differentiated structures, resulting in loss of normal growth habit.

Montane - occurring in mountains.

Mucilage - a water-soluble gelatinous slime, generally containing modified carbohydrates.

Mucro - a short sharp point on the tip of a flower or leaf. See also: drip tip.

Mucronate - ending with a triangular tip or a sharp point.

Multicellular - of an organism composed of many cells.

Multigeniculata - with many angled stems.

Mycorrhiza - a symbiotic relationship between certain fungi and the roots of plants, including orchids and many types of tree. Mycorrhiza may be ectotrophic, where the fungal hyphae invades the host roots or endotrophic where the fungal hyphae are entirely within the root cells. The fungal hyphae can help the roots to absorb essential nutrients and in some species are essential to the normal growth of the plant.

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Napiform - turnip shaped (root).

Nastic - of a movement made by a part of a fixed plant in response to a non-directional or diffuse stimulus. The direction of movement is always related to the nature of the plant part and not to the stimulus.

Natural selection - the driving force behind evolution, whereby organisms best adapted to their environment and most able to withstand environmental pressures are most likely to survive and reproduce, ensuring propagation and survival of their genes through the gene pool.

Necrosis - sudden discoloration (yellow progressing to brown) of plant tissue, followed by die back of the epidermis, caused by many factors.

Nectar - a sugary secretion produced by flowers and other vegetative parts. Nectar attracts pollinators to flowers.

Nectary - a multicellular glandular structure secreting nectar. Found in flowers and on vegetative parts in some species.

Nematode - an unsegmented roundworm with elongated rounded body, pointed at both ends. Most Nematodes are free-living in soil, fresh and salty water, but some are important parasites of animals and humans. Nematoda with over 20,000 species described, is the most common phyla of animals.

Neotype - a specimen selected to serve as the taxonomic species type when the original type material is missing.

Neri - of a species with a large number of a particular differentiated structure from the Greek nêrithmos = countless. e.g. countless spines = nerispina, nerispinus.

Neutral - i. applied to flowers with neither stamens nor pistils.
ii. applied to soils, liquids etc. which are neither acidic nor basic.

New World - coloquial- the north, central and southern Americas.

Niche - the position that an organism occupies within its environment.

Nitrogen fixing - of plants, often legumes, which are able to extract and fix nitrogen from the air by means of a symbiotic relationship with bacteria (e.g. Rhizobium species,) often in root nodules.

Nocturnal - belonging to the night, as of flowers that open at night.

Node - the place on a stem where leaves or branches originate.

Nomenclature - the study of the systematic naming of taxa, using Latin names so that they will be intelligible and uniform in all countries.

Nomen conservandum - nom. cons. - conserved name - the name of a taxon, usually one in which the name is in common usage, which is internationally agreed to be exempt from the usual rules of priority of publication.

Nomen illegitimum - nom. illeg. - a validly published name that is not in accordance with one or more rules, principally those on superfluity and homonymy.

Nomen invalidum - nom. inval. - a name not validly published according to the rules of publication.

Nomen nudum - naked name - a name published without an accompanying description or diagnosis or reference to same.

Nomen rejiciendum - nom. rej. - a name rejected in favour of a conserved name conserved or otherwise ruled as rejected.

Nothogenus - a generic name denoting an intergeneric hybrid produced by crossing plants from two different genera. Usually denoted by an 'x' before the name.
 
Nucellus - The central part of the ovule enclosing the female gametophyte.

Nucleolus - a small round densely-staining region within the cell nucleus which contains ribosomal rRNA subunits and nuclear organisers (multiple copies of genes encoding rRNA).

Nucleus - a large organelle, usually located near the center of the cell and containing the DNA.

Nuda - naked, without spines, wool etc.

Nudiflorus - naked flowers without scales, spines, or wool on the ovary and flower tube.

Nurse plant - a plant, often a shrub, which provides shelter and shade to developing seedlings of other plants.

Nut - a hard-walled fruit containing a single seed that does not split spontaneously.

Nutrient - a chemical substance that an organism ingests to enable it to survive e.g. essential minerals.

Nyctinasty - of a movement in response to changing day and night conditions.
See also: Nastic.

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Ob - a prefix to another structural descriptor of a part, indicating attachment in the opposite or inverse way to that expected from the rest of the descriptor. Hence obovate = ovate but attached at the narrow end.

Obconate - conical with the attachment at the apex of the cone.

Oblanceolate - lanceolate but attached at the narrow end.

Obligate - compulsory, essential, unable to exist under alternative conditions.

Oblique - in a diagonal position.

Obovate - ovate or ovoid but attached at the narrow end.

Obsolete - not developed.

Obtuse - with an angle greater than 90 degrees and less than 180 degrees, blunt.

Offset - a plant or plants growing from a side-shoot, rhizome or tuber that remains connected to the main plant, often easily removed for propagation.

Omnivore - an animal that eats both plants and animals.

Old World - coloquial- Europe, Africa and Asia.

Ontogeny - sequential development of an individual through all its stages.

Opposite - parts of a plant, such as leaves, arranged in pairs on opposite sides of the stem.

Orbicular - round and flat or spheroidal.

Order - a taxonomic grouping below Class and above Family. A taxonomic Order contains one or more Families.

Organ - a distinct and visibly differentiated part of a plant such as a leaf.

Organelle - a distinct sub-cellular structure, usually with a specific function and compartmentalised within its own membrane.

Organic -
i. of a mainly carbon-based molecule or chemical or chemistry.
ii. a style of agriculture where synthetic pesticides and fertilisers are not used.
iii. of food produced by organic farming methods.
iv. a marketing ploy to sell sub-standard fruit with wormholes at an inflated price.
See also: Inorganic.

Organism - a complete, living individual member of a species.

Osiris - ancient Egyptian god of vegetation, credited with introducing the skills of agriculture to the Egyptians. He became the god of the dead and the underworld, following his slaying by his brother Set and restoration to life by his wife and sister Isis. Osiris is sometimes depicted with green skin in paintings or in statues made from green stone, reflecting his aspects of agriculture, vegetation, fertility and resurrection. He was recorded as the first to make mankind give up cannibalism and credited with introducing culture of the vine and fermentation of its fruit to produce wine. This may be the oldest account of a biochemical process.
The legend of Osiris and Isis dates back to at least 2400 BC, as recounted by the Greek historian Plutarch (AD 46-120). The historian Diodorus Siculus (1st century BC) included Osiris among those who had been men, immortalised by virtue of their sagacity and good works. By this account, the legend of Osiris dates back to between 25,000 and 12,000 years ago.
The story may be derived from the Sumerian goddess of fertility, Ishtar who could grant crops and children to her devotees. Ishtar's son Tammuz rose from the dead each year, after the hot summer months, to make the land green again.

Osmosis - the movement of water through a selectively permeable membrane from a place of low solute concentration to a place of higher solute concentration.

Ovary - the female reproductive part of the plant, below the style, containing the egg cells (ovules) that after fertilisation enlarge and become seeds.

Ovate - a flattened structure (e.g. leaf) having an outline in the shape of an egg, with the stalk or point of attachment at the large end.

Ovoid - a structure with a circular cross section (i.e. not flattened as in ovate) having an outline in the shape of an egg, with the stalk or point of attachment at the large end.

Ovule - the outgrowth in a seed- plant's ovarythat develops into a seed following fertilisation of the egg cell within it. The fertilised egg cell forms a group of cells that becomes an embryo consisting of an axis, (root and stem, or hypocotyl and epicotyl) and in Cactaceae two cotyledons, with its associated protective and nutritive structures capable of developing into a plant.

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Pachycaul - of massive construction.Plants with a thick or swollen stem.

Palea - a scale.

Paleate - clothed with scales.

Paleobotany - the study ofplants that existed in former geological periods, mainly known from their fossils or pollen.

Palm - a monocotyledon of the family Palmae with an an unbranched trunk or stem crowned with large pinnate (fan-shaped) leaves. Most species are tropical or sub-tropical and some are economically important.

Palmate - divided with radial lobes like the fingers of a hand.

Panicle - a branched flower cluster, a compound raceme with pedicellate flowers. A loosely-branching pyramid-shaped cluster of flowers.

Papilla - small, rounded protruberance from any plant surface. Hence: Adj. papillose - of or relating to or resembling papilla

Papillate - covered with many tiny projections (papilla).

Papyracantha - with papery spines.

Paraphyletic - of a group of organisms sharing and including a common ancestor, but not including all the descendents of that common ancestor.
See also: monophyletic, polyphyletic.

Parasite - an organism that grows on or within another, drawing its nutrients from it e.g. mistletoe. See also commensal, symbiosis.

Parastichy - reference to the virtual spirals in plants, joining elements (tubercle, leaf, scale, floret) to their nearest neighbors. Parastichies usually come in two families winding in opposite directions. Parastichy numbers denoted by a pair (n,m) classify spiral and whorl phyllotaxes.

Paratype - additional specimens, other the holotype, cited at the same time as the original description.

Parenchyma - living undifferentiated cellular tissue with thin cell walls, which may differentiate to form other types of cell. Parenchyma cells are the most common plant cells, make and store food substances and form the pith at the centre of stems of dicotyledons.

Parietal - borne on or pertaining to the wall or inner surface of a capsule or other hollow structure. Of ovules arising from the outer wall of the ovary and pointing inwards.

Parviflora - Parviflorum - Parviflorus - with small flowers.

Parvifolia - Parvifolium - Parvifolius - with small leaves.

Paucispinus - with few spines.

Pectin - complex carbohydrates derived from poly-galacturonic acid, present in inter-cellular substances (middle lamella) and cell walls. Pectins may be divided into the three general types: protopectin, pectin and pectic acid.

Pectinate - comb-like- often used to refer to species in which the spines (or other structures) are spread out like the teeth of a comb.

Pedicel - the short stalk connecting a flower to the main stem of a plant or branches of its inflorescence. Hence: Adj. pedicellate - with stalks.

Peduncle - a stem supporting an inflorescence, or an infructescence.

Peltate - shield-shaped; of a leaf with with the leaf stalk (petiole) attached to the lower surface within the leaf margin, often near the centre.

Pendent - hanging down from a support.

Pendulous - drooping or hanging down.

Penicillate - like a tuft of hairs.

Pentagonous - with five angles.

Pepo - (Latin: = pumpkin) a berry with a firm rind, fleshy pulp, many seeds and a single locule, typified by fruits of the Cucurbitaceae.

Perennial - growing for more than two years. Cactaceae are generally regarded as perrenials.

Perfect - of an organism capable of sexual reproduction. Of a flower with both male and female flower parts.

Perianth - the combined structure comprising the calyx (sepals) and corolla (petals). In Cactaceae, the sepals and petals form an intergrading series known variously as perianth segments, tepals, sepaloids and petaloids.

Perianth segment (tepal) - the leaf like and sterile parts of a flower, especially used if these parts are not distinguishable into calyx and corolla.

Pericarp - (Greek: peri = around + karpos = fruit) the ripened and modified walls of a matured plant ovary, surrounding the seeds, including the skin and flesh.

Perisperm - the nutritional tissue contained in a seed, especially that portion which is formed outside of the embryo sac from the nucellus.

Persistant - remaining attached instead of falling away.

Pesticide - a chemical or other substance used to kill pests. Depending on the target species pesticides may be referred to as insecticides (insects), herbicides (plants), fungicides (fungi) and nematicides (nematodes). Pesticides may act on contact or require ingestion.

Petal - one of the segments of the inner perianth segments or corolla. In the Cactaceae these are actually petaloid parts of the perianth and not true petals. Petals are often brightly coloured and interior to the sepals.

Petiole - the leaf stalk.

Phaeacantha - with dusky spines.

Phenotype - the physical characteristics and appearance of an organism.

Phloem - the main food-conducting tissue of vascular plants, comprising sieve elements, parenchyma cells, fibers and sclereids.

Photosynthesis - the production of sugars from water and carbon dioxide using energy trapped from sunlight with the aid of chlorophyll.

Photonasty - of a movement in response to variation in light intensity.
See also: Nastic.

Phototaxis - movement of a whole organism or freely motile part in response to variation in light intensity and direction.
See also: Tactic.

Phototropism - bending, growth or movement of a part towards or away from light.
See also: Tropism.

Phyllopodia - a hardened, residual basal remnant of a sclerified leaf.

Phyllopodium - the whole main axis of a leaf, excluding its branches.

Phylogeny - the evolutionary history of a species or plant group.

Phylum - a major taxonomic grouping and primary division of a Kingdom, as in Kingdom Plantae, ranking above Class in size. In botany, Phylum is usually replaced by Division.

Phyllotaxis, Phyllotaxy - the study of how repeated structures such as leaves are arranged around a stem, tubercles around a cactus body. Reference to specific arrangements (e.g. (3,5) spiral phyllotaxis). Types of phyllotaxes are spiral, multijugate, decussate, distichous and whorled of which the last two are special cases of the first two. ( Gr. phyllo = leaf + taxis = arrangement )

Phytolith - a microscopic mineral particle, formed within a living plant tissue, consisting of silica (opal phytolith) or calcium oxalate and providing a durable record for archaeology and paleontology.

Phytomelanin - a papery black or blue layer or crust over the seed of plants in the order Asparagales, including Agavaceae, Aloaceae, Amaryllidaceae and Hyacinthaceae, although not present in seed of the Orchidaceae, and present as a mechanically hard brown or black layer covering seeds of other unrelated families e.g. Compositae. Nevertheless, the presence of phytomelanin is considered an important characteristic of the Asparagales. The chemical homology of phytomelanin in different plant families is not clear and its exact chemical composition is still controversial. The pigment is chemically inert and resistant to acids and bases and organic solvents. It's presence in seeds of Compositae may reduce damage from insect larvae.

Pila -
i. a pillar or pillar-like structure.
ii. a genus of African and Asian snails of the family Piladae, including around 30 species.

Pinching - removing the terminal bud, e.g. to encourage side-shoots or to prevent flower formation.

Pinnate - feather-formed. Said of a compound leaf with the leaflets along both sides of the leaf stalk.

Piperine - an alkaloid responsible for the pungent taste of black pepper, the ground fruits of Piper nigrum.
Structure of Piperine

Pistil - female organ of flower including stigma, style and ovary.

Pit -
i. a hard inner woody layer of the pericarp of some fruits (e.g. plum, cherry, olive) that contains and protects the seed.
ii. a small pockmark or depression in any structure. Hence pitted - with multiple pits.
iii. prefixed to a species name, refers to pitch or resin (e.g. Pittosporum = resinous seed).

Pitahaya - edible fruit from several species of Cactaceae (e.g. Hylocereus polyrhizus, H. undulatus, Stenocereus queretaroensis, Acanthocereus sp.) is commonly called pitahaya, pitajaya, pitaya. The fruit of all cacti is safe to eat, avoiding spines, glochids and tiny hairs present on fruit of some species, but only a few species have any culinary merit. Fruit of Acanthocereus species is said to have diuretic properties. Cactus fruit is farmed and exported from several countries including Colombia, Honduras, Palestine, Mexico and Nicaragua and is sometimes available in European and USA supermarkets.

Placentation - arrangement and attachment of ovules in the ovary.

Plant - a living organism, in the Kingdom Plantae, with cellulose cell walls and lacking a nervous system or powers of voluntary motion. Self-supporting plants use chlorophyll to capture energy from sunlight, using it to synthesise food from carbon-dioxide, water and other inorganic substances. Dependent plants (e.g. fungi, parasites, saprophytes) have no chlorophyll and use pre-existing carbon compounds as a food source. A complete plant may have roots, stems and leaves but in some cases consists of only a single leafy tissue, a series of linked cells or even a single cell. Plants are divided into flowering plants (angiosperms) reproducing through seeds and flowerless plants (gymnosperms) which reproduce by single celled spores.

Plasmodesmata - cytoplasmic strands passing between the protoplasts of adjacent plant cells through pores in the cell walls.

Plastid - a discrete structure, such as a chloroplast, within a cell often containing water-insoluble coloured pigments such as chlorophyll and associated yellow, range or red pigments.

Plumose - feather-like.

Poikilohydric - of a plant with no mechanism to prevent desiccation.

Poikilohydry - the ability of a plant to tolerate low tissue water content without damage and recover from it when wetter conditions prevail.

Pollen - the dust-like fertilising male cells of gymnosperms and angiosperms. The microscopic architecture of pollen grains is characteristic of the plant species.

Polyacantha - with many spines.

Polyancistrus - with many hooks.

Polycarpic - a plant that flowers more than once in its lifetime.

Polycephalus - with many heads.

Polypetalous - of a corolla with many separate petals.

Polyphyletic - of a group of organisms not including the most recent common ancestor, often because this common ancestor is not characteristic of the group or because the group originated from more than one evolutionary line. Polyphyletic taxa are considered "unnatural" and tend to become targets for revision by taxonomists.
See also: monophyletic, paraphyletic.

Polyploid - with more than two sets (diploid) of the basic chromosome number.

Polysaccharide - a long branched or unbranched chain of sugars linked together by glycosidic bonds. Polysaccharides are frequently molecules of great size, with molecular weights up to several million, and may serve architectural (e.g. cellulose) or food storage (e.g. starch) functions.

Pome - a fleshy fruit ( e.g. apple, pear ) having seed chambers formed from an inferior ovary surrounded by an outer fleshy part made from an enlarged hypanthium.

Porrect - extended horizontally, stretched out, pointing outward and forward.

Posterior - towards the back or towards the main axis.

Procumbent - lying on the ground but not rooting.

Proliferous - bearing vegetative offsets. Used to describe flowers or fruits that produce further flowers.

Prophyll - a rudimentary leaf at the base of a leafy shoot.

Prothallus - the growth, typical of pteridophytes, following a germination of a spore which for the purpose of sexual reproduction produces the antheridia and archegonia.

Prostrate - lying flat upon the ground.

Protein - a large biological macromolecule made from linear chains of amino acids (polypeptides) linked together by amide bonds. Proteins can have structural or functional (e.g. enzymes) roles in cells, and large proteins may be formed from multiple polypeptide subunits. The structure of each protein or polypeptide subunit is specified by a single gene.

Protoplast - the plasma membrane, nucleus and cytoplasm of the cell. A plant cell from which the rigid cell wall has been removed.

Proximal - towards the base of something near to where it is attached.

Pruinose - having a frosted appearance with a white powdery coating.

Pseudocephalium - development of wool and bristles on a mature flowering stem which continues growth. See also cephalium.

Pteridophyte - the general name for the ferns and related genera.

Pubescent - covered with short, soft downy hairs (like a peach).

Pubispina - with downy spines.
See also: arachnoid, barbate, canescence, capillaceus, capillatus, ciliate, cephalium, coma, felt, glochids, hirsute, lanate, lasiacantha, penicillate, pubescent, scabrous, villous, woolly

Pulchellus - small and beautiful.

Pulp - the juicy flesh filling the cavity of a fruit.

Pulque - a traditional alcoholic drink made in Mexico from the fermented sap of Maguey (various Agave species). Unlike beer, the fermentable carbohydrate is fructose, not starch.

Pulverulent - with a dusty coating.

Punctulate - covered with very fine points or dots e.g. the surface of a seed.

Pungent - terminating in a rigid sharp point. With an acrid, biting or sharp smell or taste.

Pyrethrum - a natural insecticide produced by Chrysanthemums, especially Chrysanthemum cinerariifolium and C. coccineum. The dried, powdered flowers of Chrysanthemums have been used as natural insecticides against lice for over 2000 years. Synthetic analogues of Pyrethrin are produced as insecticides.
Structure of Pyrethrin

Pyriform - pear-shaped .

Pyrrolizidine - an aromatic ring system found in the toxic pyrrolizidine alkaloids typical of the Genus Senecio.

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Quadrangularis - with four angles.

Quadrangulispinus - with four angled spines.

Quadricostatus - with four ribs.

Quadrispinus - with four spines.

Quinine - an alkaloid, found in the bark of the Cinchona tree, is used to treat malaria, a tropical parasitic disease carried by mosquitoes. Quinine is an essential bitter ingredient of certain drinks e.g. Indian tonic water, where it can be recognised by its blue fluorescence under ultra-violet (black) light illumination.
Structure of Quinine

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Raceme - (Latin: racemus = bunch of grapes) an elongated cluster of pedicellate flowers on an unbranched inflorescence, with the basal flowers opening first.

Radial - peripheral or positioned around the edges. In the Cactaceae, a spine positioned on the periphery of an areole.

Radial symmetry- of flowers which can be cut into equal halves along many axes passing through the flower centre.

Radiating - positioned outwards.

Radicle - an embryonic root.

Rainforest - a complex very rich community in tropical habitats with very high rainfall, dominated by trees generally supporting many epiphytes and lianas.

Rainstick - a musical percussive instrument made from a hollowed-out stem of a woody cactus, chiefly Echinopsis chiloensis and Eulychnia acida from Chile, filled with small pebbles or sand and sealed at both ends. Spines are inserted to make baffles within the hollow stem. Large numbers of rainsticks are exported from Chile to the United States and Europe as curiousities.

Raphide - (Raphis ) a needle-shaped crystal found in some plant cells, usually a crystal of calcium oxalate as a metabolic byproduct. The irritatingly sharp crystals discourage predation by herbivores.

Ray flower - one of the outer irregular florets, typically with a single tongue-shaped corolla, on flower heads of some species of Compositae (Sunflower family).

John Ray (1628 - 1705) - an emminent English naturalist who worked on classification of organisms and was the first to divide flowering plants into monocotyledons and dicotyledons. He also recognised fossils as the remains of once living organisms.

Receptacle - enlarged apex of a flower stalk bearing the parts of a flower or the florets of a composite flower. In ferns, a main stem on which sporangia arise.

Reclinate - curved backwards.

Reclining - sprawling on the ground or leaning against something.

Recurved - bent, curved or curled downwards or backwards.

Rectispinus - with straight spines.

Reflexed - abruptly curved backwards.

Regular - made from evenly, symmetrically arranged parts.

Regular flower- a radially symmetrical flower in which similar parts are equal in size, form or extent of fusion.

Reniform - an oval with the ends curved around in the same direction like a kidney.

Residual - a property of a substance, such as a pesticide, that allows it to remain in an area for a long time.

Respiration - a process of releasing energy by oxidising molecules such as glucose to carbon dioxide. Respiration produces useful reactive molecules, such as ATP (adenosine triphosphate) which activates many cellular processes by transfer of its terminal phosphate group.

Reticulate - a net-like or criss-cross pattern, often of leaf veins.

Retrorse - bent or curved backward or downward.

Retuse - a rounded termination with a small notch forming two small lobes.

Rhizoid - a filamentous root-like structure on a pteridophyte (fern) prothallus.

Rhizome - an underground stem from which roots, aerial stems or leaves can arise directly. Hence: Adj. rhizomatous - producing or possessing rhyzomes.

Rhodionin - a flavanol conjugated with the sugar rhamnose found in extracts of the genus Rhodiola.
  Structure of Rhodionin

Rhomboid - diamond-shaped.

Rib - a leaf vein. A ridge of plant-tissue thicker than its surroundings. A raised surface running vertically, sometimes spiraling, and in the Cactaceae bearing a row of areoles along its summit. Morphologically, a rib is composed of a continuous line of fused tubercles, which in some cases may be discerned as bulges in the structure.

Ricin - an extremely toxic protein found in the seed of the castor oil plant Ricinus communis, a member of the Euphorbiaceae, grown commercially for the oil content of the seed and sometimes grown as an ornamental garden annual. Less than a milligram of ricin injected into the blood stream can be fatal.

Rind - an external covering or coat such as the bark of a tree over the cambium layer, the tough outer skin of a fruit.

Riparian - of plants growing along the side or on the bottom of a watercourse, or in other aquatic areas.

RNA - ribonucleic acid- an extremely long single-stranded linear polymer, made (transcribed) as a secondary copy of the gene sequences in DNA and also found as the primary genetic material in some viruses e.g. tobacco mosaic virus.
RNA is found in cells as three basic types:

Rheotropism - bending, growth or movement of a part under the influence of a water current.
See also: Tropism.

Root - a structure usually providing a plant with anchorage and a means of absorbing water and nutrients from the substrate. Many Cactaceae have a widespread shallow fibrous root system, in addition to any taproot or tuber. This is an adaptation for scavenging water before it evaporates. See also aerial root.

Root hair- a trichome on the root epidermis made from an extension of an epidermal cell which assists with absorption of nutrients.

Rosette - a tight cluster of leaves that are arranged around a central apex and grow outward to form a radially symmetrical pattern.

Rostrate - with a beak-like projection.

Rosulate - with leaves in a rosette.

Rotate - radiating horizontally like the spokes of a wheel.

Rubber - ( caoutchouc) an organic (polyterpene) component of the latex produced within the bark of large trees in the family Euphorbiaceae (spurges) notably the Pará rubber tree (Hevea brasiliensis) native to the Amazonian rain forest in South America. Seeds from the rubber tree were sent in 1876 to Kew gardens, London, England by Henry Wickham, a local planter. Following germination of the seeds in the tropical herbarium at Kew, seedlings were exported to Ceylon (Sri Lanka) and a year later sent from Ceylon to Singapore where the method of tapping the tree for latex was developed. This avoided felling the tree to obtain latex. The rubber tree is grown commercially in Malaysia, Thailand, Indonesia, and Sri Lanka but only to a very limited extent in South America.
The latex from the rubber tree is an aqueous emulsion, also containing various proteins, and is generally coagulated by heat to produce natural rubber. Most of this is vulcanised by heating with sulphur to cross-link the polymer chains and harden the product.

Rudimentary - developed only to a primitive or early stage.

Rufous - with a reddish colouring.

Rugose - wrinkled.

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Sagittate - shaped like an arrow head with two lobes pointing backwards.

Saline - salty.

Samara - a winged fruit containing a single seed. (Latin: samara = elm seed).

Saprophyte - an organism deriving its nourishment from decaying or non-living organic material.

Saprophytic - of a free-living organism obtaining all nutrients from non-living organic sources.

Sarcody - a hyperplastic symptom in which swellings occur above and below portions of organs that are tightly encircled, as a stem might be 'choked' by a tight tie or binding or by a twining vine.

Satellite DNA - short sequences in eucaryotic DNA that are present in large numbers of repetitive copies, differ in base composition and therefore density from most of the DNA and are generally not transcribed. Often associated with the centromere.

Satellite virus - of a small virus associated with tobacco necrosis virus (TNV), which is dependent upon the TNV genome for its own replication. Of a defective virus associated functionally with another virus which it depends on for replication.

Savanna - a plant community dominated by grasses with occasional scattered trees.

Scab - a hyperplastic symptom of disease characterised by rough, crusty lesions formed by excessive cork production. A disease in which such lesions form.

Scabrous - of a leaf, roughened by tubercles, hairs or other structures on its surface.

Scale - a small leaf like structure. A narrow, triangular or spine-like lower perianth segment often found on the ovary or flower tube surface. Also see scale insect.

Scale insect - a small flat insect pest, with a waxy dorsal shield, that adheres to the plant epidermis and feeds from the plant sap.

Scandent - climbing.

Scape - a long flower stalk arising directly from a root. Adj. scapose- borne on scapes.

Scarification - a mechanical abrasive seed treatment which helps to break down a hard or impervious seed coat as an aid to germination.

Scarious - having a dry membranous appearance.

Scion - the top part of a graft.

Sclerophyll - (Greek = hard-leaved) - a woody plant with small, leathery, evergreen leaves that retain water and typically found in hot, dry climates such as Australia.

Scorch - dry brown discolouration giving a 'burnt' appearance to leaf margins as a result of infection or exposure to unfavourable environmental conditions.

Scoria - crushed volcanic rock.

Scrotiform - shaped like a hollow pouch or sac.

Scrub - a plant community dominated by low shrubs.

Seed - a sexually-produced embryo, consisting of an axis (root and stem, or hypocotyl and epicotyl) and in Cactaceae two cotyledons, with its associated protective and nutritive structures capable of developing into a plant.

Seismonastic - a movement response to a shock stimulus. Of the movement of the stamens towards the pistil when touched.

Senesce - to age naturally.
Senescence - natural aging of a part.
Senescent - of an aging part.

Sepal - one of the separate perianth leaves of the calyx.

Sericeous - silky.

Serrated - bearing straight-sided teeth. Hence Serrate - with edges like a saw blade.

Sessile - stalkless, immobile e.g. of a flower with no stalk but attached directly to the stem.

Setaceous - bearing bristles.

Setose - terminating gradually in a fine sharp bristle.

Sexual - of reproduction through the merging of male and female gametes to form a zygote which develops into a new plant.

Shrub - a horticultural term for a low bushy plant with multiple stems normally branching from the base, rather than having a single stem branching higher up as in the case of a tree.

Simple - of a leaf with an undivided blade, although it may be lobed. Of a fruit developed from a single ovary.

Sinuate - wavy-edged.

Soft Water - contains relatively low concentrations of salts (usually calcium and magnesium) that interfere with the formation of a lather with soap. Soft water from a treatment plant may contain sodium ions conferring a salty taste and making it unsuitable for irrigation.

Sp. - abbreviation for species, used as the second part of a binomial_name when the genus is known, but not the species.

Spadix - a spicate inflorescence with congested, often tiny, flowers and a stout, often fleshy or succulent axis, often more or less surrounded by a spathe. Characteristic morphology of the family Araceae.

Spathe - a large, often showy, solitary bract or pair of bracts ensheathing a spadix or other inflorescence on the same axis.

Spathulate - spoon-shaped.

Spatulate - long and thin, broadening towards the tip, like a spatula.

Specialist natural enemy - a predator which attacks only one (or a few) species. Specialist natural enemies are sometimes used as biological controls.

Speciation - a process of differentiation of a single species into one or more distinct species. This can occur through geographic isolation, where the species no longer interbreed and their characteristics slowly change under different environmental pressures.

Species - a population of individuals recognisable by morphological characteristics and unified genetic relationship, sometimes capable of subdivision into subspecies or varieties which are sufficiently closely related for interbreeding to produce offspring classified within the same species and with the same morphological characteristics.

Specific - pertaining to a species.

Sphagnum - any moss of the genus Sphagnum, sometimes used as a growing medium for e.g. epiphytes.

Spheroid - spherical with slightly flattened ends.

Spicule - a very small, fine spine or in Opuntioideae a glochid.

Spike - simple inflorescence, an elongated multiple cluster of sessile florets directly attached to an unbranched flowering stem. Hence: Adj. spicate.

Spination - the characteristics and distribution of spines, which may in some cases be distinguishing features.

Spine - a sharp outgrowth from the epidermis which may be stout and woody or fine and hair-like. In Cactaceae, always arising multiply from an areole and originating as a modified leaf. Spines are classified as central spines located centrally on the areole and radial spines around the margins of the areole. Spines protect the plant from some predators, albeit inefficiently. In some species, spines act as a drip tip where atmospheric moisture from dews, mists and rain precipitates on the spines and drips off the tip onto the soil near the base of the plant for uptake by the shallow root system.
Compare with thorns.

Splitter - coloquial - one who takes a narrow view of a genus, dividing up variant forms into individual species.

Spiral - corkscrew-shaped. Of leaves or other parts arranged around a stem or other structure with the spirals in Fibonacci number ratios.

Spore - a single, vegetative, reproductive cell formed by lower plants (cryptogams), that does not contain an embryo.

Sporopollenin - a polysaccharide biopolymer, made from cross-linked phenolics and hydrocarbons, forming a large proportion of the outer wall ofpollengrains. Sporopollenin is highly resistant to acids, bases and decay processes so identifiable pollengrains persist in ancient deposits as a fossil record of plants flowering in that era.

Spreading - growing outwardly by means of new shoots or advancing outwards by means of rooting from reclining stems. In Cactaceae, an array of radial spines projecting obliquely outwards around an areole, but not lying flat against the surface of the plant.

Spur - a usually slender hollow projection formed by the fused bases of the lower petals, often containing nectar, in some flowers or a short fruit-bearing stalk.

Stalk -
i. a slender or elongated fleshy structure that supports a plant or plant part such as a leaf or flower or a fungus.
ii. waste plant material consisting of stem, seed pod etc. separated from harvested seeds.

Stamen - pollen-bearing male sexual organ of a flower, consisting of anther and filament.

Staminate - of a male flower possessing stamens but not a pistil.

Staminode - a sterile stamen.

Starch - an insoluble high molecular weight (typically several million kDa) polysaccharide formed from beta-D-glucose units linked together with alpha-1,4' linkages (compare with cellulose). Amylose starches are long unbranched molecules whyle amylopectins are branched polysaccharides with alpha-1,6' linkages at the branch point. Starches can be broken down easily into glucose, as required, by amylase enzymes in the tissues and are the principal food storage substance of plants. Starch can be recognised by forming a characteristic blue colour with iodine.

Stellate - star-shaped.

Stem - the main axis of a plant which may carry other parts.

Sterile - incapable of engaging in the process of sexual reproduction.

Stigma - receptive surface or structure for pollen at apex of style or pistil. One style may bear multiple stigmas, in Cactaceae usually 3-20.

Stipe - a short supporting stalk.

Stipitate - having, supported or elevated on a stipe.

Stipulate - of a part furnished with stipules. Of a stem or leaf stalk (petiole) with a pair of growths resembling leaf stipules at the base.

Stipule - a small leafy growth, often found in pairs, at the base of a leaf or stalk.

Stolon - a prostrate basal branch above or below the ground which can root and produce new plants at its tip.

Stoma - (Pl. stomata) - a very small opening or pore through the plant's epidermis, through which respiration and transpiration occurs, surrounded by two guard cells. The stoma is usually capable of active opening and closing through changes in shape of the guard cells. Stomata are found on the plant body of cacti and on any leaves.

Stone - the hard woody inner layer of the pericarp of fruits known as drupes ( e.g. cherries, peaches, plums ) within which is the seed.

Stratification - a process of exposing sown seeds to low, near freezing temperatures to imitate natural over-wintering as an aid to germination. During the process, chemical inhibitors of germination are broken down.

Strophiole - (syn. Caruncle - ) of a band or twisted band; a crestlike, corky excrescence about the hilum of certain seeds, derived from the funicle.

Strychnine - a bitter alkaloid poison found in the seeds of the asian tree Strychnos nux-vomica native to India, Sri Lanka and Australia. Strychnine has been used as a poison for several hundred years and causes characteristic convulsions.

Striate - a surface marked with longitudinal (lengthwise) lines, in some cases exhibiting slight ridges or furrows.

Style - structure, usually slender connecting ovary and stigma.

Sub - a prefix to a descriptor meaning "almost".

Sub-class - a subdivision of a class.

Subgenus - a subdivision of a genus into morphologically recognisable groupings of species.

Subspecies - a subdivision of a species, recognisable by morphological characterisitics, but not isolated by genetic barriers from other members of the species. Sometimes designated as a variety.

Subulate - slender or tapering and flattened into a narrow elipse in cross-section, awl-shaped.

Succulent - juicy (Latin: succus = juice,sap), fleshy plants that store water in specially adapted thickened or swollen organs such as leaves, stems or roots.

Suckers - shoots or small plants arising from the base of a larger plant.

Sulco - of a plant or part with a groove or furrow (Latin: sulcus = furrow or groove).

Superior - above other parts, higher in rank or position.

Sustainable use - the careful exploitation of natural resources without destroying them.

Symbiosis - (Greek: = living together) - a balanced partnership in which two dissimilar organisms live together for their mutual benefit e.g. the algae and fungae jointly forming lichens. See also commensal and parasite.

Sympetalous - (gamopetalous), of a flower with a corolla composed of partially or wholly fused petals forming a tube or funnel.

Synonym - an invalid name according to the International Code for Botanical Nomenclature.

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Tactic - of a movement made by a whole organism, or by a freely motile part such as a gamete, in response to a directional stimulus which has a direct bearing on the direction of the elicited response.
See also: Phototaxis

Tannin - a heterogeneous group of astringent phenolic substances, widely distributed in plants, and commercially used in tanning, dyeing and preparation of ink.

Taproot - a primary root growing straight down from a plant, and larger or longer than the branching fibrous roots. Often a thick storage organ as in a carrot.

Tardiflora (-um) - late flowering.

Tardifolia (-um) - late into leaf.

Taxon - a formally described category of individuals, distinct by some visible characteristics.

Taxonomy - the system and practice of classification.

Tectora (-um) - of roofs.

Teeth - sharp, pointed triangular structures arising on leaf margins.

Temperate - a climatic zone between boreal and tropical. Regions between the tropic of Cancer and the Artic Circle or the tropic of Capricorn and the Antarctic Circle.

Tender - of a plant plant that needs a minimum temperature of 60°F, although occasional brief periods of lower temperatures may be tolerated.

Tendril - a slender leafless side-shoot, often coiling around other objects, produced by many climbing plants as an aid to climbing and support.

Tenui - slender, thin.

Tepal - any of the modified leaves making up a perianth.

Terminal - borne at the end of a stem, branch or other structure e.g. terminal spine located at the end of a leaf.

Terrestrial - growing in or on the ground.

Tessellate - a surface patterned like a mosaic or pavement.Hence tessellata.

Testa - the outer protective seed-coat.

Testicular - in the form of two oblong bodies .

Tetra - four, as a prefix.

Tetradploid - with twice the normal complement of chromosomes.

Thermotropism - bending, growth or movement of a part under the influence of a heat source.
See also: Tropism.

Thallus - a multicellular plant body, usually flat and not organized into roots, stems, leaves or vascular system.

Thigmotropism - or- Haptotropism - a growth response to a touch stimulus.
See also: Tropism.

Thorn - a sharp woody outgrowth from the epidermis which unlike the spines of Cactaceae contains vascular tissue and arises from the underlying tissues (phylogenetically as a modified stem). Because of this, breaking a thorn off the plant damages the surrounding tissue.
Compare with spines.

Throat - the visible portion of a flower between the limb and tube.

Thyrse - a dense cylindrical or ovoid inflorescence, a compact panicle; branched, the main axis indeterminate and the lateral branches determinate (i.e. with a terminal flower) or as a cyme.

Tissue - any part of an organism consisting of aggregated cells with a similar structure and function.

Tomentum - a layer of matted woolly threads on the surface of a plant. Often the hairs are white, giving the surface a silvery appearance. Latin="cushion stuffing"
    Tomentose - of a surface covered with tomentum.
    Tomentous - of a surface covered with tomentum.
    Tomentosum - epiphet of a plant covered with tomentum.


Tortuous - twisted.

Tracheid - a basic primitive unit of the xylem (fluid-conducting tissue), consisting of a single elongated cell with pointed ends and a thick, pitted secondary cell wall composed of cellulose thickened with lignin. The mature tracheid is dead and empty of cytoplasm. Tracheids are found in all vascular plants and are the only conducting elements in gymnosperms and ferns.

Tracheary - of conducting tissues containing tracheids and vessels.

Trans-Pecos - of territory in Texas west of the Pecos River.

Transpiration - loss of water vapour through the plant's stomata. C4-metabolic adaptations in the Cactaceae and other succulents allow transpiration to be minimised.

Transverse - across or at right angles to the vertical.

Trap - a structure designed to catch and detain animal prey.

Tree - a plant with a single distinct trunk between the ground and first branch.

Traumotropism - bending, growth or movement of a part as a response to wounding.
See also: Tropism.

Trichome - a hair-like structure growing at one end from the plant's epidermis. Trichomes have numerous forms including branched or unbranched hairs, scales and glands.

Tridentate - forked into three points.

Trifoliate - a compound leaf with three leaflets.

Trigger hair - a specialized structure found in the traps of certain carniverous plants which causes the trap to activate in response to stimulation.

Trigonous - with a three-cornered, triangular cross section.

Tropism - Tropic - of a movement by a fixed part of a fixed plant towards or away from a stimulus such as gravity, heat or light, the direction of movement being determined by the direction from which the stimulus originates. A tropism is caused by a positive or negative growth response on the side of the organ nearest to the stimulus relative to the side furthest from the stimulus, and the whole organ then bends away or towards the stumulus respectively. See also: Chemotropism, Galvanotropism, Geotropism, Hydrotropism,Phototropism, Rheotropism, Thermotropism, Thigmotropism. Traumotropism,

Truncate - ending suddenly as if cut cleanly off.

Trunk - the main woody stem of a tree supported and directly attached at the lower end to the roots and at the upper end supporting the branches.

Tube - a narrow flower structure formed by fusion of the tepals.

Tuber - a thick, fleshy underground modified root or stem section used for storage of food or water, as in a potato.

Tubercle - small, rounded prominence or knob-like protusion from the surface. In Cactaceae a roughly pyrimidal protrusion from the stem surface, with an areole at or near its summit. Hence: Adj. tuberculate.

Tuberculate - having tubercles.

Tuberous root - a generally undistended fibrous root system with thickened fleshy sections scattered along its length. Not a taproot or caudex.

Tubular - in the form of a hollow cylinder.

Turbinate - shaped like an inverted cone or top.

Turgid - swollen by some internal force, usually by fluid uptake.

Turgor pressure - outward force exerted on a cell wall by water taken up into the cell by osmosis.
See also: wall pressure

Type - the permanently preserved specimen or specimens on which the species or sub-species description is based.

Type locality - the place where the type specimen was collected.

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Umbel - a flat-topped or rounded inflorescence in the shape of an umbrella with individual pedicels arising close together.

Umbilicus - a scar or depression on the summit of a fruit after the floral parts are shed.

Uncinate- uncate - terminated by a sharply curved hook. Hence uncinatus - with hooked spines.

Undulate - wavy with alternately concave and convex regions. Hence undatus, undulatus - with wavy margins, undulated.

Under glass - grown in the greenhouse or, in the case of a cutting, with a jar or cloche placed over it.

Unequal - asymmetrical.

Ungui - claw-like. Hence unguispinus - with claw-like spines.

Uni - one, singular, as a prefix.

Uniseriate - (Latin: uniserialis) arranged in a single row, such as a single row of seeds in a pea pod. Having one line or series.

Unitegmic - with a single covering over a part e.g. ovule.

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Vagans - wandering.

Valida - strong, healthy, well developed.

Valve - a segment into which a dry fruit dehisces.

Variegated - with patches or stripes of different colours, often yellow or reddish. Hence variegata - of a plant exhibiting variegation.

Variety - a naturally occurring subdivision of a species representing individuals with distinct but minor variations in their characteristics. The taxonomic rank between subspecies and form.

Vascular - of tissues containing vessels for conveying fluids and minerals.

Vascular bundle - a compact group of conducting bundles composed of xylem and phloem and surrounding tissues, occurring in stem, leaf and flower. In Cactaceae a clear ring of vascular tissue is on a cross section cut across the stem. This woody material also has a structural function and forms the supporting skeletons of many cacti.

Vegetative - growth of leaves and stems as opposed to flowers. A method of non-sexual reproduction by means of offsets, cuttings.

Vein - a strand of vascular tissue in a flat organ such as a leaf.

Venation - the arrangement of veins within a structure.

Ventricose - distended or inflated.

Vermiculate - worm-shaped.

Verrucose - of a surface covered with warty protrusions.

Versicolor - variable in colour.

Verticillate - arranged in whorls.

Vesicle - a hollow structure or cavity which may be macroscopic like a bladder or microscopic as in a sub-cellular organelle.

Vessel - (trachea) - an efficient fluid conducting structure in most angiosperm xylem, which has evolved from the primitive tracheids found in gymnosperms and ferns by loss of the end walls of the cells so that each vessel runs for several cell-lengths, reinforced by rings and spirals of cellulose fibrils thickened with lignin.

Vestigial - reduced to a rudimentary structure.

Villous - with long soft hairs.

Vine - a plant with a weak trailing stem which relies on other plants or structures for vertical support.

Violacea - violet coloured.

Viperina - snake-like.

Virgate - slender, twiggy or wand like.
Hence: Virgatus (-a, -um).

Virid (-is, -i) - green.

Viridiflorus (-a) - with green flowers.

Viridescens - becoming green.

Viridifolius - with green leaves.

Viridifuscus - green-brown.

Viridissimus - very green.

Viridulus - somewhat green.

Virus - a simple parasitic micro-organism consisting of little more than a package of genetic material (DNA or RNA) in a protein or lipid envelope, capable of invading the host's cells and replicating only by harnessing their biochemical machinery. Some viruses carry several genes for synthesis of virus-specific proteins. Others (e.g. potato spindle tuber virus) consist of a circle of DNA which is too small to carry any structural genes.

Viscaria - sticky.

Viscid (-a, -m) - covered with a sticky secretion.

Vittata - with lengthwise stripes.

Viviparous - germinating or spouting from a seed, bulbil or bud while still attached to the parent plant.

Vulgaris - common.

Vulpinus - fox-like.

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Wall - See: cell_wall,   Exine,   Pericarp

Wall pressure - inward force exerted by a cell wall on the cell contents by virtue of the elastic properties of thecell walland by pressure from surrounding cells.
See also: turgor pressure

Wardian Case - a glazed terrarium created by Dr Nathaniel Bagshaw Ward (1791-1868) in about1829 for transporting plants and growing delicate mosses and ferns.

Wax - a diverse group of naturally-occurring greasy, hard, or soft and moldable high molecular weight solid substances of animal, plant or mineral origin. Wax may contain saturated hydrocarbons, esters of higher fatty acids, and higher alcohols. Most natural waxes contain a wide range of molecular sizes and therefore soften over a wide temperature range instead of melting at a specific temperature, as do substances of a uniform molecular size.

Weed - a plant growing in the wrong place.

Whorled - of leaves or other parts, not alternate or opposite but placed in a circle around the stem.

Wilt -
i. to droop, usually due to loss of turgor pressure.
ii. any of several diseases that cause plants to wilt and die.

Window - a translucent portion of the leaves of some succulent plants which allows light to penetrate to the photosynthetic layers.

Wood -
i. a hard fibrous substance composed of cellulose bonded together with lignin formed as the main fluid conducting tissue or xylem making up the greater part beneath the bark of the trunk, branches and roots of trees, shrubs and other woody plants.
ii. a dense growth of trees, somewhat smaller in extent than a forest.

Wood gum - xylan

Wood sugar - xylose

Woody - made of or resembling wood. Of plant tissues hardened by accumulation of lignin.

Woolly - thickly covered with long hairs.

Wort - archaic Middle English word for any plant or herb, often one considered medicinal or otherwise useful in combination with a word describing the use e.g. lousewort, lungwort, glasswort
Old English: wyrt = herb, root.

Wrinkled - creased or folded up irregularly in every direction.

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Xanthophyll - a class of orange oxygenated carotenoid pigments in which one or more double bonds of a carotene have been substituted with hydroxy, methoxy, carboxy, epoxy and oxo (ketone) groups. Like carotene, xanthophylls assist photosynthesis.

Xenogamy - (Greek: xenos = stranger + gamos = marriage) cross pollination.

Xenograft - a graft from a different species

Xeranthemoides - with a dry appearance.

Xeromorphic - structural features of plants, xerophytes, adapted to dry conditions with a thickened cuticle or hairs protecting against moisture loss or with the appearance of such plants.

Xeriscape - an arid landscape or water-conserving garden in which xerophytic plants grow. A desert garden.

Xerophyte - a plant adapted to dry conditions.

Xylan - a yellow water-soluble gummy polysaccharide component of the hemicellulose of woody tissues, made from (1-4) linked xylose monomers. Derivatives may have arabinose (arabinoxylan) or 4-O-methylglucuronic acid (glucuronoxylan) side chains.

Xylose - (Greek: Xylon = wood) a white crystalline pentose (five-carbon) sugar isomeric with ribose, produced by hydrolysis or fermentation of xylans in straw or wood and an important dietary constituent of herbivores. Used in foods for diabetics as it can not be metabolised by humans. Non-fermentable by normal yeast.

Xylem - the main upward water-conducting tissue in vascular plants characterised by tracheary elements. Xylem may also be a supporting tissue, especially secondary xylem (wood).

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Yarda - Yarfa - a peaty bog.

Yeast - a unicellular Ascomycete that typically multiplies by a budding process, although some yeasts (e.g. Sacharomyces pombe) multiply by symmetrical division. Sacharomyces species are important mediators of the commercial fermentation of carbohydrates to alcohol.

Yield - measurable produce of economic value, related to a specified crop or animal, or to a defied area, and to a period of time.

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Zebrinia - with striped leaves.

Zebrinus (-a, -um) - zebra-striped.

Zephyr - of the west.

Zoophilous - pollinated by animals, especially other than insects e.g. bats.

Zonatus - with concentric markings.

Zone - a distinct geographic region exhibiting characteristics distinct from neighbouring regions.

Zygomorphic - bilaterally symmetrical.

Zygote - a fertilised reproductive cell formed by the merging of two gametes, before any cell division occurs.