Description from Flora of China
Carex supina Wahlenberg var. costata Meinshausen; C. supina subsp. korshinskii (Komarov) Malyschev; C. supina var. korshinskii (Komarov) Kükenthal.
Rhizome slender, creeping or obliquely ascending. Culms densely tufted, 15-35 cm tall, slender, compressed triquetrous, smooth on lower part and scabrid on upper part, with few yellowish brown or red-brown bladeless sheaths and rudimentary sheaths at base, rudimentary sheaths usually disintegrating into fibers. Leaves shorter or longer than or equaling culm, blades 1-2 mm wide, slightly stiff, scabrous on upper surface and margins, sheathed. Involucral bracts scale-shaped, lowermost sometimes long awned at apex. Spikes 2 or 3(or 4), uppermost female spike and male spike approximate, lowermost female spike rather remote; terminal spike male, clavate or lanceolate, 1-2.5 cm, sessile; lateral spikes female, ovate or subglobose, 5-10 mm, densely several to 10-flowered, sessile. Female glumes brown, ovate, ca. 3 mm, with 1 midrib, margins white hyaline, apex acute. Utricles yellow, first obliquely patent, later slightly divergent, elliptic or obovate, inflated trigonous, 3-4 mm, leathery, shiny, smooth, obscurely veined, base obtuse, apex abruptly contracted into a very short beak, orifice obliquely truncate or emarginate. Nutlets gray-brown, tightly enveloped in utricle, elliptic, trigonous, 2-2.5 mm, apex mucronate; style base slightly thickened; stigmas 3. Fl. and fr. Jul-Sep.
Grasslands, mountain slopes, sand dunes; 700-1300 m. Gansu, Heilongjiang, Liaoning, Nei Mongol, Shaanxi, Xinjiang [Korea, Mongolia, Russia (Far East, E Siberia)].