Rhizome long creeping, subcylindric. Culms 10-60 cm tall, acutely trigonous, scabrous above, clothed with bladeless sheaths at base. Leaves shorter than culm, blades linear, 2-4 mm wide, flat, margins scabrous, apex acuminate. Involucral bracts glumelike. Spicate inflorescence cylindric or subconic, 2-5.5 × 0.7-1.5 cm, usually interrupted below; spikes 10-20, terminal and lower spikes female, middle and upper ones male or androgynous (or entirely female), ovate, 5-9 × 2-3 mm; female spikes broadly ovate, 7-10 × 5-7 mm. Female glumes pale ferruginous-brown, ovate-lanceolate or oblong-ovate, ca. 3.5 mm, margins white hyaline, apex acute. Utricles stramineous, longer than glume, broadly ovate, plano-convex, 3.5-4 × 1.8-2 mm, thinly membranous, spongy, slender, several veined on both faces, base rounded, upper margins serrulate winged, apex abruptly contracted into a beak, orifice 2-toothed. Nutlets yellow-brown, loosely enveloped, elliptic or oblong, plano-convex, 1.5-1.8 mm, base shortly stipitate; style base slightly thickened; stigmas 2. Fl. and fr. May-Jun.

Swamps, riverbanks, meadows; 100-700(-1700) m. Gansu, Hebei, Heilongjiang, Jilin, Liaoning, Nei Mongol, Shaanxi, Shandong, Shanxi, Xinjiang [Japan, Korea, Mongolia, Russia (Far East, E Siberia)].