Plants usually cespitose, short to long rhizomatous. Culms erect or lax, 5-35(-40) cm. Leaves: sheaths and bases from previous year´s leaves usually absent; ligules rounded or acute; blades glabrous adaxially. Inflorescences unispicate (very rarely with short, sessile lateral spike of same sex), mostly erect, ellipsoid; primary inflorescence bracts leaflike, rarely scalelike, shorter or longer than inflorescences. Scales red-brown to purple, ovate to lanceolate, to 3.5 × 1.5 mm, shorter than, equal to, or longer than perigynia, margins hyaline, narrow to broad, central midrib extending midway or to scale apex, apex acute to obtuse. Perigynia red-brown, ovate to lanceolate, to 4 × 1.6 mm, as wide as subtending scale, apex tapering or rounded, distal 3/4 hirsute with white hairs; beak 0.1 mm, orifice circular; rachilla absent. Achenes 1-2 × 0.6-1.2, tightly enveloped by perigynia, occupying full width and at least 3/4 length of perigynia. 2n = 62. Subspecies of Carex scirpoidea grow in a variety of habitats in northern North America. Taxa previously recognized as varieties or separate species are treated here as subspecies of C. scirpoidea. Within the C. scirpoidea complex, all subspecies have the same chromosome number, possess similar achene micromorphology and leaf anatomy, interbreed in greenhouse experiments, and have morphologic characteristics that mostly fall within the normal range for C. scirpoidea.
Dioecious; stems 1-4 dm, surpassing the lvs, 1-few together from a rhizome; main lvs 1-3 mm wide; peduncle often with a minute bract ca 1 cm from the top; spike 1, erect, slender, 1-3 cm; pistillate scales deep brown, a little shorter and much narrower than the perigynia, thinly hairy; perigynia appressed-ascending, obovate-oblong, 2.5-3 mm, densely short-hairy, 2-keeled, otherwise virtually nerveless, subtriangular in cross-section, the minute beak 0.2 mm; achene trigonous; ±filling the perigynium; no rachilla; 2n=62-68. Dry soil, especially in calcareous regions; irregularly circumboreal, widespread in n. N. Amer. and s. in our range to the n. parts of N. Engl., N.Y., and Mich. Our plants are var. scirpoidea.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.