Japan Flora: Stems slender and branched; submersed leaves lin­ear to broadly so, 4-7 cm. long, 4一6(-8〉mm. wide, rounded to obtuse at apex, undulate and serrulate, sessile and obtuse or subrounded at base and sometimes slightly clasping, 3-nerved; stipules thinly membranous, about 10 mm. long; peduncles 2-5 cm. long; spikes lax and few-flowered, 1-15 cm. long; nutlets broadly ovate, about 3 mm. long, obscurely toothed on the median ridge of back; style elongate, about 2 mm. long. May-July. Ponds and shallow rivers.

Hokkaido, Honshu, Shikoku, Kyushu. Worldwide except South America.