Plants densely cespitose. Culms 20-90 cm; vegetative culms inconspicuous with few leaves clustered at apex. Leaves: sheaths white-hyaline or green-veined, sometimes papillose, summits U-shaped, not distally expanded; distal ligules 2.2-6 mm; blades 3-4 per fertile culm, 11-25 cm × 1.7-4.2 mm. Inflorescences mostly dense, brown, 1.1-3 cm × 5-14 mm; proximal internode 1-4 mm; 2d internode 1.4-3.4 mm; proximal bracts scalelike, with bristle tips shorter than inflorescences. Spikes 3-10, usually overlapping, ovoid to globose, 4-10 × 3-7 mm, base rounded or truncate, apex rounded. Pistillate scales reddish brown, usually with green or whitish to brown midstripe, lanceolate, 2.5-3.5 mm, shorter and narrower than perigynia, apex acuminate or acute. Perigynia ascending to ascending-spreading, light to dark reddish brown, conspicuously 3+-veined abaxially, faintly or basally 1-3-veined adaxially, winged to base, ovate or elliptic, plano-convex, 2.5-3.8 × (1-)1.2-2 mm, 0.35-0.45 mm thick, 1.9-2.5 times as long as wide, margin flat, including wing 0.2-0.5 mm wide, 1b ciliate-serrulate at least distally; beak reddish brown at tip, flat, ± ciliate-serrulate, abaxial suture with reddish brown-hyaline margin, distance from beak tip to achene 1.2-2.2 mm. Achenes ovate or elliptic, 1-1.3 × 0.6-0.9 mm, 0.3-0.4 mm thick. 2n = 68, 70. Fruiting early summer. Wet places with calcareous or neutral soils, gravelly lakeshores, stream banks, meadows, forest seeps; 0-2100 m; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask.; Alaska, Colo., Conn., Idaho, Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Oreg., Pa., S.Dak., Utah, Vt., Wash., Wis., Wyo. In addition to typical perennial behavior, Carex bebbii may reach reproductive stage from seed in a single season, thus behaving as a facultative annual. Carex athrostachya and C. crawfordii may share this reproductive feature.