Rhizome short, long stoloniferous. Culms 25-60 cm tall, tufted, acutely trigonous, smooth, scabrous in lower part of inflorescence, clothed at base with yellow-brown or brown bladeless sheaths disintegrating into reticulate fibers. Leaves shorter than or equaling culm, flat, 2-4 mm wide. Lowest involucral bract leaflike, longer than or equaling inflorescence, sheathless, remaining ones setaceous. Spikes 3-5; upper 1 or 2 spikes male, narrowly cylindric, 2-5 cm; remaining spikes female, occasionally some becoming androgynous and bearing several male flowers at apex, narrowly cylindric, 15-30 × 2-4 mm, densely many flowered, lower spikes with peduncles, upper sessile. Female glumes dark brown or purplish, oblong-lanceolate, ca. 2.5 mm, margins narrowly white hyaline, yellow-green 3-veined costa excurrent into a mucro, apex acute, rarely obtuse. Utricles gray, light green, or yellow-green, longer than glume, ovate, ca. 3 mm, membranous, ferruginous punctate, obscurely veined, base contracted into a short stipe, apex gradually attenuate into an obscure beak, orifice entire. Nutlets slightly tightly enveloped, obovate-oblong, ca. 1.5 mm; style base slightly thickened; stigmas 2. Fl. and fr. Apr-May.

Lakesides, marshes, wet places. Anhui, Heilongjiang, Hubei, Hunan, Jiangsu, Jilin, Liaoning, Nei Mongol, Shaanxi [Japan].