A genus of plants in which the twining annual stems arise from an often massive subterranean tuber; the tuber contains much starch and is known as a yam. The leaves have palmate main nerves and nervation as fine as a spider's web. Some species yield steroids used for oral contraceptives. There are about 600 species, of the tropics and subtropics, 1 species occurring in Europe.
Subjects: Plant Sciences and Forestry.