Japan Flora: Fronds floating, obliquely ovate-elliptic, 3-5 mm. long, 2-4 mm. wide, rounded at tip, rounded or very obtuse at base, entire, green, 3-nerved, sessile; root single, with an acute root-cap; ovules orthotropous, erect Common in ponds and paddy fields.
Hokkaido, Honshu, Shikoku, Kyushu. Widely distributed in tropical regions.