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:
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.