The Order Dioscoreales consists of mainly-tropical flowering monocotyledons, with around 600 species within the Dioscoreaceae (yam family) and about 35 species in other genera. A few members of the Dioscoreales are native to temperate Europe and America. Most species are twining vines with large underground starchy succulent tubers or surface caudexes but a few herbs are also included. Leaves are often heart shaped or lobed.
The Dioscoreaceae (yams) include important agricultural crops that have been cultivated for thousands of years, although careful preparation is often required to inactivate or remove bitter toxins from the tubers. The best modern cultivars have been selected to minimise the presence of toxins. Some yams (e.g. Yellow Guinea Yam D. cayenensis) are probably hybrids of garden origin with no known wild equivalents.
Use is made of steroid precursors in the tubers of some species (Dioscorea villosa, Dioscorea mexicana), from which the constituents of the progesterone birth control pill were synthesised.
Several species produces large succulent caudexes on the surface of the soil and are frequently seen in collections of succulent plants.