Japan Flora: Stems simple or slightly branched; leaves all submersed, linear-oblong to lanceolate, 8-12 cm. long, 1-2.5 cm. wide, 7- to 13-nerved, obtuse at base, with a mucro 2-3 mm. long at apex, obscurely serrulate，conspicu­ously undulate on margin, the petioles 1.5-3 cm. long; the stipules 2-4 cm. long; spiles rather densely flowered, 3-5 cm. long; nutlets about 3 mm. long, 3-ridged on back, the median ridge more prominent and entire. June-Oct. Ponds and shallow rivers.

Hokkaido, Honshu, Shikoku, Kyushu. Ryukyus, China, Formosa, Malaysia, and India.