Culms obtusely trigonous, to 35 cm × 1.5 mm, scabrous distally. Leaves: sheaths with blades, to 2 cm, rough, fronts spotted red-brown apically, ladder-fibrillose, orifice red-brown, slightly prolonged beyond blade and sheath, leathery; blades 35 cm × 3 mm, margins rough; proximal blades blue-green, densely papillose. Inflorescences to 10 cm; peduncle of staminate spike to 2.5 cm; proximal bracts about equaling inflorescences; staminate spikes 1-3; pistillate spikes 2-3, to 4 cm × 4 mm. Scales red-brown with green midrib and hyaline margins, obovate, apex obtuse or with short mucro to 0.3 mm, equaling perigynia and narrower. Anthers to 2.5 mm. Perigynia ascending, green, spotted red-brown on distal 1/2, sessile, 2.2 × 1.4 mm; beak orifice purple-brown, glabrous. Achenes brown, 1.6 × 1.1 mm. Fruiting Jul. Abandoned quarries, ditches, marshes, wet forest edges; 0-800 m; introduced; N.S., Ont., Que.; Mich., N.Y.; Europe; introduced New Zealand. Carex flacca occurs throughout Europe, especially on calcium-rich soils. It is sparsely introduced in North America, but appears to be increasing. The species is superficially similar to and may be mistaken in the field for one of the smaller species of sect. Phacocystis.
Vigorously colonial by creeping rhizomes, 2-6 dm; main lvs 2-5 mm wide; terminal spike staminate, 1-3 cm, long-peduncled; pistillate spikes 1-3 cm; pistillate scales ovate, with broad, pale midvein and brown sides, acute to short-acuminate or mucronulate; perigynia elliptic-obovoid, minutely hispidulous distally, nerveless or nearly so, even the lateral ribs inconspicuous, abruptly narrowed to a minute beak; achene rounded-trigonous, bent-apiculate. Native of Eurasia and n. Afr., intr. in fields and meadows from N.S. and Que. to Ont. and N.Y. (C. glauca)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.