Rhizomes 0.8-1.9 mm thick, shoots often arising 2-several per cluster, many nodes without shoots. Culms bluntly trigonous, (8-)15-40 cm, smooth-angled distally. Leaves: basal sheaths pale to dark brown; sheaths with hyaline inner band, apex not prolonged, glabrous; ligules 0-2.8 mm; blades 1-3(-3.5) mm wide. Inflorescences dense, headlike, 1.2-3.5(-4.5) cm, 1/2+ as wide as long (if pistillate); spikes 6-20(-25), usually unisexual; staminate spikes lanceoloid; pistillate spikes ovoid. Pistillate scales pale brown to ± whitish hyaline, hyaline margins, lanceolate to ovate, (4.3-)4.7-7.5 mm, apex acute to acuminate, satiny to ± dull. Anthers (2.5-)2.8-3.9 mm, apiculus bristly (30X). Perigynia brown, essentially veinless, usually stipitate, ovate to broadly elliptic, ± plano-convex, (3-)3.5-4.2(-4.8) × 1.2-2.1 mm, dull; beak (0.9-)1.2-1.9 mm, apex hyaline, friable, oblique or obscurely bidentulate.
Fruiting Jun-Aug. Prairie, sagebrush grasslands, forest openings, meadows, marsh edges, stream banks, in dry to wet soils, various open, successional and usually moist habitats, tolerant of alkaline soils; 500-3500 m; Alta., B.C., Sask.; Ariz., Calif., Colo., Idaho, Mo., Mont., Nebr., Nev., N.Mex., N.Dak., Oreg., S.Dak., Utah, Wash., Wyo.; Mexico (Baja California).
The stigmas of Carex douglasii are very long and form a tangled mat that persists essentially until the perigynia mature, giving a distinctive appearance to pistillate inflorescences of the species. Though the plants are uniform in appearance superficially, the perigynia are quite variable in shape and size.
The Missouri locality is an introduction in a railway yard.
Stems 1-3(-4) dm, smooth, scattered on long, slender, sympodial rhizomes; lvs basally disposed, 1-2.5 mm wide, flat or involute; dioecious; spikes sessile, inconspicuously bracteate, ovoid-fusiform, 1-1.5 cm, closely aggregated into a rhomboidal or ovoid to subcylindric head 1.5-4.5 cm; perigynia mostly ±hidden by the scales, rather narrowly elliptic to elliptic-obovate, planoconvex, becoming sharp-edged and serrulate distally, obscurely multistriate and with evident marginal nerves, 3.5-4.5 mm, including the prominent, 1-1.5 mm beak; achene lenticular; 2n=60. Dry soil; Man., Io., and Nebr. to B.C., Calif., and N.M.; intr. along railways in Mo.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.