Plants densely cespitose. Culms 20-100 cm; vegetative culms with few leaves clustered at apex. Leaves: sheath summits U-shaped; distal ligules 2.3-4.8 mm; blades 3-5 per fertile culm, 10-32 cm × 1.4-3(-3.5) mm. Inflorescences arching or nodding, dense or open, green, yellow, or brown at maturity, 1.5-6 cm × 5-20 mm; proximal internode 2-12 mm; 2d internode 2-13 mm; proximal bracts scalelike, with bristle tip. Spikes 3-10, distinct, ellipsoid, 7-16 × 3-9(-13) mm, base acute to short-attenuate, apex acute to rounded. Pistillate scales hyaline brown, occasionally with green or gold midstripe, lanceolate, 3.4-4 mm, shorter and narrower than perigynia, apex acuminate. Perigynia ascending or rarely widely spreading, golden brown, conspicuously 5-veined on each face or fewer adaxially, winged to base, lanceolate, flat except over achene, 4.2-6.8 × 1.2-2 mm, length at least 3 times width, 0.35-0.55 mm thick, margin flat, including wing 0.2-0.6 mm wide; beak pale to golden-brown at tip, flattish, ciliate-serrulate, abaxial suture with white or golden brown hyaline margin, distance from beak tip to achene 2.2-4.8 mm. Achenes ovate or elliptic, 1.3-1.7 × 0.7-0.9 mm, 0.3-0.4 mm thick. Carex scoparia is variable and may, in fact, be a complex of at least 2 species. Given current understanding, 2 varieties are recognized:
From Flora of Indiana (1940) by Charles C. Deam
Common in marshes and open swampy places; occasional in low open woods and on sandy lake borders. This sedge is frequently the dominant plant in marshes or "sedge meadows" where it is usually associated with Juncus effusus var. solutus, Juncus Dudleyi, and Carex vulpinoidea.
Tufted, 3-10 dm, aphyllopodic; main lvs 1.5-3 mm wide, shorter than the stems; sheaths ventrally hyaline; spikes 3-8, gynaecandrous, 8-14 mm, ovoid to fusiform or subglobose, pale greenish to dull-stramineous or tan, sessile in an open to more often condensed spike 2-4 cm; bracts inconspicuous, or the lowest one to about as long as the infl; pistillate scales lance-ovate, acuminate or shortly awn-pointed, narrower and shorter than the perigynia; perigynia lanceolate, very flat, 4-5.5 נ1.5-2 mm, 2.5-3 times as long as wide, much wider than the achene, several-nerved on both sides, wing-margined and serrulate, tapering gradually to the ill-defined flat beak; achene lenticular, 1.3-1.8 נ0.7-0.8 mm; 2n=60, 64, 68. Open swamps, wet meadows, and shores; Nf. to Fla., w. to B.C., Oreg., and N.M.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.