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 .