Forest & Kim Starr
Family
Dioscoreaceae
Botanical Name
Dioscorea
Plant Common Name
Yam
General Description
A highly diverse genus found mainly in the tropics and subtropics, Dioscorea comprises more than 600 twining, tuberous herbaceous perennials, including the yams. Winged yam (D. alata), lesser yam (D. esculenta), Guinea yam (D. rotundata) and Indian yam (D. trifida) are all important crops. Other members of the genus are grown for ornamental or medicinal use.
These often vigorous climbers typically have heart-shaped, netted-veined leaves alternating along branched or simple stems. The stems may be smooth, winged, or prickly. Clusters of small, inconspicuous, often fragrant flowers are produced at the stem tips or in the leaf axils. Flowers are usually dioecious (male and female flowers on separate plants). Male and female plants often differ markedly in form. The fruit is a capsule which splits to expel winged, wind-dispersed seeds.
Plants grow from a tuber, which is typically underground but may be exposed. Some Dioscorea bear small storage organs (bulbils) in the leaf axils, which can root and produce new plants after dropping.
Generally, these vines grow best in full to partial sun and fertile, friable soil. In frost-free zones they typically go dormant during the dry season. In more temperate zones dormancy occurs in winter. Some are rampant growers that can engulf and overpower surrounding plants entirely if not controlled. Plants may spread rapidly by bulbils; some are considered invasive or noxious weeds.
Hundreds of edible yam varieties exist, differing in tuber consistency, color, and size. They are usually harvested at the end of the rainy season in tropical and subtropical areas or in late summer in more temperate climes. Edible yams are versatile and are eaten mashed, roasted, stewed, fried, or pounded into flour. They can be added to savory or sweet dishes but most often accompany meat or vegetables.
Often grown as ornamentals are D. discolor, with handsome mottled leaves, and D. elephantipes, whose massive exposed tuber resembles a tortoise shell. D. macrostachya (the source of an artificial progesterone) and D. villosa are among the several Dioscorea that have been used medicinally.
The genus is named for the ancient Greek physician Dioscorides.
