Water chestnut

Eleocharis dulcis, the Chinese water chestnut or water chestnut, is a grass-like sedge native to Asia, tropical Africa, and Oceania. It is grown in many countries for its edible corms. The water chestnut is not a nut but rather an aquatic vegetable that grows in marshes, under water, or in mud. It has stem-like, tubular green leaves that grow to about 1.5 m . The water caltrop, which also is referred to by the same name, is unrelated and often confused with the water chestnut.

Source: Wikipedia