无柱黑三棱 wu zhu hei san leng

Stems floating, 30-50 cm or more, slender. Leaves floating, 30-40 cm × 1-3 mm, transverse section semilunate. Racemes 5-7 cm, axis straight; male heads 1 or 2, smaller; female heads 2 or 3, lowest one pedunculate. Male flowers: perianth segments 2-2.5 mm, attenuate toward base; filaments short; anthers oblong, ca. 1 × 0.5 mm. Female flowers: perianth segments linear to obtriangular, ca. 1.5 × 1-1.3 mm, serrate-lobate at apex; ovary elliptic; styles absent or inconspicuous; stigmas elliptic, ca. 1 mm. Fruit broadly obovoid, ca. 4 mm. Fl. and fr. Jul-Aug. 2n = 30.

Lakes, ponds, swamps; ca. 1500 m. Heilongjiang, Jilin [Japan, Korea, Russia; Europe, North America].