Plants colonial, long-rhizomatous. Culms 30-60 cm, scabrous to smooth distally. Leaves: proximal sheaths fibrillose, bladeless, brown- to reddish purple tinged, 2-4.5 mm diam.; ligules 2-10 mm, longer than wide; largest blades green, flat, 4-45 cm × 2.5-6 mm. Inflorescences 6-19 cm, 1.4-2.2 times longer than proximal bract; proximal bracts 2-9 cm; sheath 0.6-2 cm, blade 1.5-7 cm; proximal spikes pistillate or androgynous; lateral spikes cylindric, 1.5-3.5 cm × 7.5-11 mm; terminal 1-3 spikes, staminate. Pistillate scales purple or brown, apex rounded or obtuse. Perigynia densely arranged, green to light brown, 2-ribbed and finely veined, 4.2-6.8 × 1.5-2.5 mm, with low, broad papillae; beak purple tinged, mouth hyaline, obliquely bidentate, asymmetrically flared, 0.8-1.8(-2.2) mm. Achenes light to dark brown, 2.2-2.8 × 1.4-2.3 mm.
Fruiting early-mid summer. Thin woods with sandy soils; of conservation concern; 30-1200 m; Conn., Del., Maine, Md., Mass., N.H., N.J., N.Y., Pa., R.I., Va., W.Va.
Carex polymorpha, rare throughout its range, is of conservation concern (L. A. Standley and J. L. Dudley 1991).
Stems stout, 3-6 dm, in dense colonies from stout rhizomes, aphyllopodic, the basal lvs reduced to bladeless sheaths; stem-lvs firm, flat, 3-5 mm wide; terminal spike peduncled, staminate, 1-3 cm, often with 1 or 2 smaller ones at its base; pistillate spikes 1 or 2, erect, widely separated, the lower peduncle longer than the upper; bracts with conspicuous loose sheaths and well developed blades usually exceeding the spikes; pistillate scales ovate, much shorter than the perigynia, with purplish-brown sides and conspicuous green center; perigynia numerous, crowded in several rows, glabrous, 4-5.5 mm, stoutly ellipsoid, obscurely nerved except the 2 prominent lateral keels, the prominent beak straight or somewhat outcurved, 1.3-2.2 mm, with a very oblique orifice; achene broadly obovoid- trigonous, loosely enveloped. Dry open woods, mostly in acid soils; Me. to Md. and W.Va.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.