YAM  

Yams are the tuberous roots of several vines of the genus Dioscorea, family Dioscoreaceae. Used like potatoes, they are a major tropical root crop and are grown in warm, temperate, and tropical regions around the world. Generally, the starchy yam tubers resemble the SWEET POTATO, but the two are not even distantly related. The roots of D. sativa and D. alata are the most important commercial yams. Many varieties occur within these species, and the resulting yams may weigh up to 45 kg (100 lb) and have brown or black skin and flesh that is white, purple, or red. The usual method of propagation is to use the crowns of the large tuberous root or to plant whole small tubers. The climbing vines are supported on stakes or on a trellis. The plants are spaced 30 to 60 cm (12 to 24 in) apart in rows. The roots are harvested after they reach a suitable size and can be stored for several months at temperatures of 12 deg-15 deg C (54 deg-58 deg F). In the United States yams are grown as vegetables only in Florida. As an ornamental, however, the Dioscorea vines, especially the cinnamon vine, are often grown in greenhouses for their handsome green leaves.