Yam

True yams are starchy tubers of tropical plants that are related to the grasses and lilies, a dozen or so cultivated species of Dioscorea from Africa, South America, and the Pacific with varying sizes, textures, colors, and flavors. They are seldom seen in mainstream American markets, where “yam” means a sugary orange sweet potato. True yams can grow to 100 lb/50 kg and more, and in the Pacific islands have been honored with their own little houses. They appear to have been cultivated as early as 8000 BCE in Asia. Many yams contain oxalate crystals just under the skin, as well as soap-like saponins, which give a slippery, frothy quality to their juices. Some varieties contain a toxic alkaloid called dioscorine that must be removed by grating and leaching in water. Yam tubers help their plants survive drought, and they have a longer pantry life than cassava or taro.