Note: Information is dated. Do not rely on it.Yam. A plant belonging to the genus Dioscorea, characterized by herbaceous twining stems, seeds with membranous wings, and fleshy, tuberous roots. The yams are natives of the tropics and are largely cultivated for food both in the East and West Indies. The roots are starchy or sweet and used as food like the sweet potato. In some species the roots attain great size. The winged yam, Dioscorea alata, has roots that attain the weight of 25 pounds. The best known American species is the common West Indian yam, Dioscorea sativa, which has heart shaped leaves and bears bulbous tubers in the axils of the leaves. This is grown in some of the southern United States. The yam is prepared for eating by boiling or roasting, and is much esteemed as food in the countries where it is grown.