Description from Flora of China
Carex riparia Curtis var. rugulosa (Kükenthal) Kükenthal; C. smirnovii V. I. Kreczetowicz.
Rhizome with rather thick stolons. Culms 50-80 cm tall, obtusely trigonous, smooth on lower part, scabrid on upper part, clothed with red-brown and bladeless sheaths at base, remnant sheaths usually disintegrating into reticulate fibers. Leaves nearly equaling culm, blades 3-5 mm wide, flat, stiff, sheathed. Involucral bracts leafy, lowermost involucral bract equaling or slightly longer than inflorescence, upper involucral bracts rather short, shortly sheathed. Spikes 4-6; terminal 2 or 3 spikes male, distance between spikes short, narrowly lanceolate, 1-3.5 cm, nearly sessile; remaining spikes female, remote, cylindric or oblong-cylindric, 2-4 × ca. 1 cm, densely many flowered, laxly flowered at base, with ca. 1 cm peduncle. Female glumes pale ferruginous laterally, ovate, 3.5-4 mm, membranous, 3-veined, apex acute. Utricles brown-green or brown-yellow, obliquely patent, longer than glume, elliptic or ovate-elliptic, obtusely trigonous, 5-6 mm, corky, glabrous, several veined abaxially, base rounded, apex abruptly contracted into a slightly broad and short beak, orifice half-rounded concave and shortly 2-toothed. Nutlets slightly tightly enveloped, elliptic or ovate-elliptic, trigonous, ca. 3 mm, base shortly stipitate; style slightly long, flexuose, persistent, base not thickened; stigmas 3. Fl. and fr. Jun-Jul.
Riversides, grasslands at lakesides, strands. Hebei, Heilongjiang, Jilin, Nei Mongol [N Japan, Russia (Far East)].