yam

yam, 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.

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yam

Any of several plant species of the genus Dioscorea (family Dioscoreaceae, or yam family), native to warmer regions of both hemispheres. A number of species are cultivated for food in the tropics; in certain tropical cultures, notably of West Africa and New Guinea, the yam is the primary agricultural commodity and the focal point of elaborate ritual. The edible tuberous roots, which vary in taste from sweet to bitter to tasteless, are eaten as cooked starchy vegetables. Often boiled and then mashed, they may also be fried, roasted, or baked. True yams are botanically distinct from the sweet potato, though in the U.S. the names are commonly interchanged. Dioscorea mexicana contains a chemical that can suppress ovulation in humans and is used as the basis for birth-control pills. The so-called yam bean is the legume jicama.