Rhizome short, tussock-forming. Culms tufted, 30-75 cm tall, acutely trigonous, slender, scabrous, clothed at base with reddish brown, slightly lustrous, bladeless sheaths disintegrating into fibers. Leaves subequaling culm, blades linear, ca. 2 mm wide, flat, margins scabrous. Lowest involucral bract leaflike, equaling or longer than inflorescence, sheathless. Spikes 3-5; upper 1 or 2 spikes male, narrowly cylindric, 0.8-2.5 cm, terminal spike with peduncle; remaining spikes female, occasionally some becoming androgynous and bearing several male flowers at apex, oblong to narrowly cylindric, 10-30 × 3-4 mm, densely many flowered, with short peduncles or subsessile. Female glumes purple-black, narrowly elliptic, 1.5-2 mm, green 1-3-veined at middle, scabrous on veins, margins narrowly white hyaline, apex obtuse. Utricles light green, longer than and much broader than glume, elliptic, rarely obovate or suborbicular, plano-convex, (1.8-)2.2-3 mm, densely minutely papillose, veined, apex abruptly contracted into a short beak, orifice emarginate. Nutlets tightly enveloped, broadly obovate or obovate, plano-convex, ca. 1.5 mm; style base not thickened; stigmas 2. Fl. and fr. Jun-Jul.

Moist places, marshes; ca. 600 m. Heilongjiang, Jilin, Nei Mongol [Korea, Russia (Far East, E Siberia)].