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a genus of plants, usually lianas, of the family Dioscoreaceae. They are dioecious perennial herbs, less often subshrubs, with tubers or rhizomes. The leaves are usually alternate and simple. The flowers are small, diclinous, and gathered into racemes or spikes. The fruit is a pod. There are more than 600 species in the tropics and sub-tropics, rarely in the temperate zones. In the USSR there are two species—D. caucasica in western Transcaucasia and D. polystachya in the southern parts of the Far East. Their rhizomes contain saponins; the preparation diosponin has been suggested for treating atherosclerosis The species D. batatas, D. alata, and D. saliva, among others, are cultivated for their edible tubers and are better known by the name yams.