ヒシ科ヒシ属の一年草で、学名は Trapa japonica (syn. rapa bispinosa var. iinumai)。英名はありません。
The "Hishi" (Trapa japonica) belongs to Trapaceae (the Water caltrop family). It is an annual herb that is distributed 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 Japanese name is derived from the shape of the fruit, which has long been used for food. I used to eat them when I was a child while picking them from the pond. It is called "菱" in Taiwanese Chinese and "丘角菱" (qiu jiao ling) in Chinese.