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Definition: yam from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

Any of a group of climbing plants cultivated in tropical regions; the starchy tubers (underground stems) are eaten as a vegetable. The Mexican yam (D. composita) contains a chemical that is used in the contraceptive pill. (Genus Dioscorea, family Dioscoreaceae.)

The elephant's foot yam, a wild variety that produces edible tubers of up to 661 lb/300 kg each, was found not to be extinct after 40 years, by UK botanists from the Millennium Seed Bank in May 2001. It is found only in the Northern Cape Plateau, South Africa.

Summary Article: yam
From The Columbia Encyclopedia

common name for some members of the Dioscoreaceae, a family of tropical and subtropical climbing herbs or shrubs with starchy rhizomes often cultivated for food. The largest genus, Dioscorea, is commercially important in East Asia and in tropical America. The thick rhizomes, often weighing 30 lb (13.6 kg) or more, are used for human consumption and for feeding livestock. A number of species of Dioscorea are cultivated for extraction of diosgenin, a female hormone precursor used in the manufacture of the contraceptive pill. In the United States, cultivation of yams for food is restricted to the South, but the wild yam (sometimes used medicinally) is indigenous farther north, and another species, the cinnamon vine, is cultivated as a decorative plant. The sweet potato, which belongs to the morning glory family, is sometimes erroneously called yam. The S African elephant's-foot (Testudinaria elephantipes), also called Hottentot bread and tortoise plant, is sometimes grown in greenhouses; its large rootstock was formerly eaten by the natives. Yams are classified in the division Magnoliophyta, class Liliopsida, order Liliales, family Dioscoreaceae.

The Columbia Encyclopedia, © Columbia University Press 2018

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