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.

yam Tubers of perennial climbing plants of Dioscorea spp.: D. rotundala white yam, and D. cayenensis, yellow or Guinea yam, water, trifoliate, or Chinese yam. A major food in parts of Africa and also the Far East. A 150‐g portion is a source of vitamins B₁ and C; provides 5 g of dietary fibre; supplies 200 kcal (840 kJ). In the USA sweet potatoes are sometimes called yams.