Japan Flora: Plant tufted; culms 10-40 cm. long, obtusely angled, glabrous; leaf-blades 1.5 mm. wide; spike solitary, terminal, 1-2 cm. long, the staminate linear, longer or shorter than the pistillate, about 1 mm. across，the pistillate oblong, about 3 mm. across, densely many-flowered; pistillate scales elliptic, very obtuse, rusty-brown; perigynia about as long as the scales, 1.5-2 mm. long, spreading, broadly ovoid, inflated, trigonous, nerved, abrupdy very short-beaked with an entire tip.  Apr.-June. Wet places.

Honshu, Shikoku, Kyushu; rather common. Korea, Manchuria, and Ussuri.