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).