The tubers of some wild yams produce compounds called saponins that can be used to make cortisone and certain other drugs. The word yam is commonly used to refer only to yam tubers. Their flesh is white or yellow. Yam plants are climbing vines. Their stems bear small green flower clusters.
Yams require hot, moist weather and a long growing season.
Western Africa produces about half of this crop. Yams also grow in India and in the countries of Southeast Asia and the Caribbean Sea. The United States grows no yams due to the cold climate and short growing season. Yams belong to the yam family, Dioscoreaceae. Common edible yams include Dioscorea alata and D. rotundata.