Japan Flora: Plant small, slender, with filiform sometimes branched stems; floating leaves broad-lanceolate to ovate-oblong, 1.5-2.5 cm. long, 3-8 mm. wide, acute or abruptly obtuse, rather acute at base, 7-nerved, entire, the petioles shorter than the blades, submersed leaves filiform, 3-6 cm. long, 0.3-1 mm. wide, very acute; stipules thinly membranous, 6-10 mm. long, their edges overlapping; peduncles 1-2 cm. long, slightly thickened above; spikes 1-1.5 cm. long, more or less dense; nutlets sessile, broadly obovate, about 2 mm. long, 3-ridged on the back, the median ridge acute, with a few obtuse teeth; style rather short. June-Oct. Ponds and paddy fields; 

Hokkaido, Honshu, Shikoku, Kyushn. Korea, China, Ussuri, Formosa, India, and Malaysia.

var. miduhikimo (Makino) H.Hara. Leaves broadly lanceolate to narrowly ovate-elliptic; median ridge of the nutlet destitute of teeth; style short. June-Oct. Ponds and paddy fields; Honshu, Shikoku, Kyushu.