"Hiru-mushiro" (Potamogeton distinctus) belongs to Potamogetonaceae (the Pondweed family). It is a perennial herb that is distributed throughout Japan, Taiwan, the Korean Peninsula, and China. It grows in ponds, streams, and rice paddies. It used to grow widely as a weed in paddy fields. It has linear submerged leaves that float on the surface of the water, and it produces yellow-green spikes from May to October. The Japanese name "蛭蓆" is derived from the floating water leaves as a seat on which a leech can sit and rest. In Taiwanese Chinese, it is called "異匙葉藻", and in Chinese, it is called "眼子菜" (yan zi cai).