True yams are tropical root crops from the family Dioscoreaceae. This plant is Dioscorea alata. Yams produce hairy tubers (bottom center of the picture) with a small corm at the top of the tuber. Yams are rarely grown in the U.S. and are not an important crop. However, in parts of S. America, Africa, and Asia yams are a staple crop. In addition to being used for food, yams are a source of steroidal sapogenins that were once widely used by the pharmaceutical industry until synthetic steroids were developed.