Rhizome short, indurate. Culms tufted, 20-70 cm tall, erect, acutely trigonous, scabrous above, clothed with brown bladeless sheaths at base. Leaves shorter than or subequaling culm, blades linear, 2-4 mm wide, flat, soft, margins serrulate. Involucral bracts setaceous at base, other bracts glumelike. Spicate inflorescence cylindric, 2.5-6 cm; spikes 10-16(-20), gynaecandrous, pale green, ovate, 5-10 × 4-6 mm, densely flowered, upper spikes contiguous, lower ones distant. Female glumes pale brown, ovate, 2.2-2.8 mm, green 1-veined, apex acute. Utricles longer than glume, ovate or ovate-lanceolate, plano-convex, curved, 3.4-3.7 mm, membranous, spongy, 5-7-veined abaxially, 4- or 5-veined adaxially, base rounded, margins very narrowly scabrous winged, apex gradually narrowed into a ± long beak, orifice 2-toothed. Nutlets pale brown, loosely enveloped, oblong or oblong-ovate, slightly biconvex, ca. 1.5 mm, base cuneate, shortly stipitate; style base not thickened; stigmas 2. Fl. and fr. May-Jun. 2n = 68.

Wet grassy places along streams. Anhui, Heilongjiang, Henan, Jiangsu, Jilin, Liaoning, Zhejiang [Japan, Korea, Russia (Far East)].