"Hishi" (Trapa japonica) belongs to the Trapaceae (the Water caltrop family). It is an annual herb that is distributed to all over Japan, as well as the Korean Peninsula, China, Ussuri and Taiwan. This herb grows in ponds or swamps, and its roots spread in mud. The leaves are broad lozenged and float on the water surface. The petioles are swollen and serve as a bladder. The white, small, four-petaled flowers bloom from July to October. The fruits are diamond and have been used as food from long ago.