Dioscorea

Dioscorea is a genus of dioecious climbers in the Dioscoreaceae or yam family. The plant base is a rootstock or caudex supporting vine-like stems that bear leaves, flowers and fruits. The caudex is thickly tuberous, rhizomatous or woody, above or below ground or partly above. The bark on the caudices may be coarse or showing reticulated patterns. The vines growing from them may be over 10 m long, few or in tangled multitudes.

The alternate or sometimes opposite leaves are flat, stalked and variable, including heart-shaped, arrow-shaped, rounded, lobed or digitately divided forms. The leaf venation is reticulated.

The small and fairly insignificant flowers are mostly unisexual, growing solitary or paired, in racemes, spikes or panicles. The perianths comprise six segments arranged in two concentric whorls of three, mostly fused at the base. There is sometimes an urn-shaped or bell-shaped basal tube to the flowers. Male flowers are six-lobed with six stamens sometimes united in a column and sometimes with rudimentary style. The female flowers have six free segments with staminodes sometimes present. The inferior ovary has three locules and three short styles with tips sometimes split in two.

The fruit capsules are three-angled or three-winged and three-valved, while single-seed, indehiscent fruits occur in some. The fruits simplify recognition of female plants, as the fruits often persist on the plants for long. The winged seeds are compressed.

There are about 600 species of Dioscorea worldwide, growing in tropical and subtropical regions, 16 of which occur in southern Africa. The genus was named after Pedanios Dioscorides, well-known Greek herbalist of the first century AD.

Some of these plants contain steroids and alkaloids, yielding medicinal products like cortisone and ingredients of contraceptives. Some non-South African yams are staple foods in Africa, Asia and Central America, such as the yellow yam and the white yam, both subspecies of Dioscorea cayenensis. Porcupines eat the soft pith inside the caudices of some species. Some dioscoreas are poisonous, although their yams can be detoxified via certain procedures.

The plant in picture is D. sylvatica photographed near Sani Pass (Leistner, (Ed.), 2000; Smith, et al, 2017; Vlok and Schutte-Vlok, 2015; Pooley, 1998).