is a yam a starch
Yams are the source of the chemical diosgenin, a precursor of progesterone, cortisone, and other medically important steroids. The collection of plants for the production of diosgenin is licensed in several parts of the world. The true yam is about 20 percent starch and as a food is very similar to a potato.True yams (Dioscorea spp., Dioscoreaceae) are the third most important tropical root crop after cassava (Manihot esculenta, Euphorbiaceae) and sweet potato (Ipomoea batatas, Convolvulaceae).he water yam is a species from south-eastern Asia that is commonly cultivated. The Chinese yam, or Chinese potato, also known as cinnamon vine, is cultivated as an ornamental climbing vine but is also an important food plant; its thick tubers reach a length of about 1 m (3 ft).