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.
Stems 3-10 dm, densely clustered on a very short rhizome; lvs septate- nodulose (especially the sheaths), mostly 4-10 mm wide; lvs subtending the pistillate spikes sheathless or only shortly sheathing, at least the lowest one generally several times as long as the infl; spikes several, crowded, sessile or nearly so, or the lowest one more remote and slender-pedunculate; lower spikes pistillate, the upper staminate or androgynous; pistillate spikes 1.5-5 נ1.5-2 cm; pistillate scales conspicuous, shorter and narrower than the perigynia; perigynia numerous, densely crowded in 8+ rows, widely spreading or the lowest ones retrorse, glabrous, shining, evidently 6-13-nerved, 7-10 mm, firm-walled but somewhat inflated, ellipsoid to subglobose and often somewhat oblique, narrowed to a prominent, slender, smooth beak 2-3(-4) mm with short (0.3-0.9 mm) teeth; achene dark brownish, narrowly trigonous, 2 mm, loose in the lower part of the perigynium, the persistent, bony style becoming contorted with maturity; 2n=70. Swampy woods and wet meadows; Que. to B.C., s. to Del., Md., Ind., Io., and Oreg.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.