Plants cespitose; rhizomes very short or inconspicuous. Culms trigonous in cross section, 10-105 cm, smooth distally. Leaves: basal sheaths dark reddish brown; ligules longer than wide; blades mid to dark green, flat to W-shaped, widest leaves 3-10 mm wide, glabrous. Inflorescences 3-20(-35) cm; proximal bract 19-70(-100) cm, (2.5-)3-9 times longer than inflorescence; proximal (2-)3-6 spikes pistillate, ascending to spreading, at least the distal erect, ca. 20-150-flowered, cylindric; terminal 1(-3) spikes staminate, slightly if at all elevated beyond summit of crowded pistillate spikes. Pistillate scales narrowly ovate, 2.4-4.5 × 1.1-1.8 mm, shorter than perigynia, margins entire, apex acute to acuminate, awnless. Perigynia mostly reflexed at maturity, often green or straw colored, strongly 6-13-veined, veins running into beak, ovate, 6-10 × (1.6-)2.1-3.4 mm, apex abruptly tapered; beak 2.1-4.5 mm, bidentulate, smooth, teeth straight, 0.3-1.1 mm. Stigmas 3. Achenes pale brown, symmetric, not indented, trigonous, smooth. Fruiting Jun-Aug. Swamps, wet thickets, often along streams, marshes, sedge meadows, shores of streams, ponds, and lakes; 0-1900 m; B.C., Man., N.B., Ont., Que., Sask.; Conn., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mont., N.Y., Oreg., Pa., Utah, Vt., Wash., Wis., Wyo. Very rarely, specimens appear to be intermediate between Carex retrorsa and C. lupulina or C. lupuliformis; they are likely hybrids.