Japan Flora: Perennial with roughened stolons; leaves linear, 4-10 mm. wide, abruptly acute, flattened, elongate, densely and prominently serrulate, 5-veined; spathe about 1.3 cm. long, loosely enveloping the ovary at anthesis; ovary smooth, linear, about 12 cm. long in fruit; seeds narrowly obovoid, 15 mm. long. Aug.-Oct. Shallow rivers and ponds.