Water yam is a vigorous, perennial, climbing plant, producing annual stems up to 15 metres long from a very large tuberous rootstock . These stems scramble over the ground, or twine into the surrounding vegetation . The stem is quadrangular, winged, and twines right-handed. The plant is widely cultivated in tropical areas for its edible root . A very polymorphic species, originating in SE Asia and not found wild, it was dispersed by humans over the Pacific and Indian Oceans in prehistory, and is now widespread in the Region and pantropicsDioscorea alata, also known as purple yam, ube, or greater yam, among many other names, is a species of yam (a tuber). The tubers are usually a vivid violet-purple to bright lavender in color (hence the common name), but some range in color from cream to plain white. It is sometimes confused with taro and the Okinawa sweet potato (Ipomoea batatas cv. Ayamurasaki), although D.
alata is also grown in Okinawa where it is known as beniimo . With its origins in the Asian tropics, D. alata has been known to humans since ancient times. Dioscorea alata fruit plants in Kerala
Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves . The uncooked tuber of this species is toxic, and is said to produce narcosi . Saponin is present and cooking renders the tubers safe to eat