water chestnut

Any of several perennial water plants of the genus Trapa (family Trapaceae), native to Europe, Asia, and Africa, or their edible, nutlike fruit. The water caltrop (T. natans) has two sets of leaves—long, feathery, rootlike, submerged leaves and a loose rosette of floating leaves attached to leafstalks 2–4 in. (5–10 cm) long. The small fruit usually has four spiny angles. The Chinese water chestnut (Eleocharis tuberosus) is a member of the sedge family.