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Dioscoreaceae Linnaeus 1753 - Wild Yams
Named after the Greek physician, Dioscorides

The Dioscoreaceae is a group of 8 genera and over 600 species, including many caudiciforms or species with an underground tuberous root. A climbing vine with heart shaped or lobed leaves, and without tendrils, is produced from the tuber and may be a seasonal growth, or a more permanent one, depending on the species. Plants in this family are unusual among monocotyledons in having net-veined leaves. In some species e.g. D. bulbifera aerial tubers are produced from leaf axils along the vine. Male and female flowers are produced on separate plants (dioecious). The fruit is a berry, capsule or samara, and the seeds are usually winged and flat.

This family includes the edible yams which were cultivated in Africa and Asia around 10,000 years ago and are important crops in tropical countries. The starchy tubers of many species of yam, especially African yams, contain toxins and require careful preparation before they can be eaten safely.

Dioscorea

The species most commonly seen in collections of succulent plants is the "Elephant's Foot" Dioscorea elephantipes (was Testudinaria elephantipes). Tubers of wild yams, especially Dioscorea villosa and Dioscorea mexicana contain steroid precursors (Diosgenin) from which the constituents of the old progesterone birth control pill were synthesised.

Cultivation: A free-draining sandy soil rich in humus suits these plants. I like to put a layer of grit immediately under the caudices of D. elephantipes and D. sylvatica. I have never noticed any pests on my Dioscoreas, perhaps thanks to their content of bitter alkaloids such as Diosgenin.

Dioscoreas and similar vining plants are best grown wound around a climbing frame. Buy a larger frame than appears necessary. It will soon be covered. Triangular frames as illustrated in the photograph of Testudinaria elephantipes tend to touch at their top, encouraging tendrils to explore and a row of plants to become hopelessly entangled. Pyrimidal frames made of black wire and suitable for a 12 in pot or larger help to confine the growth of vining plants to the footprint of the pot. Some careful weaving of the stems around the support is needed for a neat effect.

	*D. alata* (Purple Yam, Winged Yam) is the most widely distributed cultivated yam in Africa, SE Asia, Polynesia and W. Indies, although grown in smaller quantities than the African Yam D. rotunda. Because it develops and propagates itself via small bulbils formed in the leaf axils, Purple Yam has become an invasive species in some Southern USA states. The common name, winged yam refers to prominent ridges along the angular stem. The lumpy tubers (right) have a purple-brown surface, but when cut the starchy core of some varieties has a violet tinge. Considerable selection has occurred among the cultivated varieties. The wild yams are bitter and poisonous.
*D. bulbifera* (Air Potato) produces aerial tubers from leaf axils along the 20 ft vine. The stem is rounded. The potato-sized bulbils are easy to harvest and more important than the tuberous roots. As every leaf has the potential to produce a bulbil, this plant has become a pest in warm climates such as Florida. However, it is a popular crop for small gardens.

Dioscorea caucasica Lipsky 1892
This climbing plant has green stems bearing heart-shaped, prominently veined leaves with a matt-green surface. Stems, especially flower stems are slightly pubescent. The small yellow flowers are on the end of a prominent three-winged seed pod. Native to the Caucasus and fully winter-hardy.

Dioscorea communis Syn. Tamus communis (Black Bryony)

In England and Europe, the native wild yam (Black Bryony) is moderately common in ancient hedgerows and woodland margins. From a large underground tuber arises a seasonal twining vine (right) with characteristic glossy heart shaped leaves and small greenish-yellow flowers followed by bright red glossy berries. The berries often persist after the foliage has withered, making a fine display in the Autumn.

While the leaves are similar to those of the African "Elephant's Foot," the smooth tuber can not be successfully grown on the surface for display. However, it grows well outdoors in a large pot or bedded out. Watch out for snails which can dig deep into a pot, eat into tubers and lay hundreds of eggs for another generation.

The plants are either male or female, so careful selection of cultivated plants is needed to obtain a display of the attractive glossy red berries. To grow the seeds, mascerate the berries in water and separate the seeds from the pulp to discorage moulds. After sowing the seeds, place the pot outside where it will be exposed to a winter's cold, after which the seeds germinate freely.

The tubers and berries are very poisonous, yet "Black Bryony" figured in traditional herbal medicine as a powerful diuretic. The result of an overdose was a painful death. External application of the mascerated tuber was safer and used to treat bruises, chillblains, gout and rheumatism.

Note: To confuse the unwary amateur herbalist, the native English "White Bryony" is a Cucurbit with different toxic and herbal properties. Both Black and White Bryony are sometimes found growing together in hedges and woodland margins. White Bryony was cultivated in the past as a counterfeit of Mandrake root, a continental tuberous plant from the Family Solanaceae with a long history of use as an anaesthetic and in childbirth.

		*D. deltoidea* from Northern India is a seasonal vine with black stems bearing heart-shaped leaves with prominent veins. The inflorescence is a raceme of many, well-spaced tiny (one-eighth inch) green flowers. Seed capsules are dry, 3 winged pods. The tubers are fully hardy.

D. dumetorum (Bitter Yam) is a popular crop in W. Africa as its cultivation requires little effort. Cultivars are less toxic than the wild forms which are sometimes used as poisons.

Dioscorea elephantipes Syn: Testudinaria elephantipes (Elephant's Foot)
This species is the most commonly seen Dioscorea in collections of succulent plants. The distinctive caudex is covered with greyish-brown corky bark that becomes deeply fissured into polygonal segments with age. In the late summer a seasonal growth of a twining black branching stem is extruded from the caudex and climbs and twines around any convenient support or other nearby plants. After a considerable length of stem has been produced very glossy heart shaped leaves develop on the numerous side branches. Considerable variation in the leaves may be seen between different cultivated plants. Clusters of tiny yellow flowers are produced after the leaves.

D. elephantipes typically stays in leaf until the Spring and requires careful watering throughout the winter. It tolerates cool, frost-free conditions. I also like to dampen the dormant caudex periodically to stop it from drying out in hot weather and to remind it to break dormancy in late Summer. Feed with high nitrogen fertiliser to encourage growth of the caudex.

D. nipponica from Japan has lobed, prominently veined leaves with a matt-green surface. Although the vine is seasonal, the tubers are sufficiently hardy to be planted in the garden. It produces dry, 3-winged seed pods.

D. rotunda (White Yam) Syn. D. cayenensis (Yellow Yam)
is native to Africa and the most important cultivated edible species with over 200 cultivars. An edible yam purchased from a food store can certainly be sprouted, but in my experience requires a great deal of heat. The brittle angular green stems blacken quickly as the glasshouse cools in the autumn.

D. sylvatica Ecklon 1908
from Uganda to Zimbabwe and the South African Cape Province, where it grows in forest margins. The plant produces a very large-lobed, flattened caudex with smooth or cracked corky bark. It is not uncommon in collections of caudiciforms. The vining top growth can extend to 20ft and in the greenhouse needs to be constrained to a climbing frame. The foliage is more or less permanent and seems to grow at any time of the year. The matt green, heart-shaped leaves and stems die periodically and are renewed throughout the year. The inflorescence is a raceme of greenish-yellow flowers. Seed capsules are dry, 3 winged pods.

An undemanding plant that should be fed with high nitrogen fertiliser to encourage the caudex to grow. A little water keeps it in growth during the winter, but if kept dry the leaves are deciduous. Cool, frost free conditions are sufficient. Plants are variable and several varieties have been described.

D. tokoro has green stems bearing heart-shaped, prominently veined leaves with a matt-green surface. Although the vine is seasonal, the tubers are sufficiently hardy to be planted in the garden and survive the English Winter.

The Wild Yam PageDioscoreaceae

Dioscoreaceae Linnaeus 1753 - Wild YamsNamed after the Greek physician, Dioscorides

Dioscorea

Dioscorea communis Syn. Tamus communis (Black Bryony)

The Wild Yam Page
Dioscoreaceae

Dioscoreaceae Linnaeus 1753 - Wild Yams
Named after the Greek physician, Dioscorides