Plants loosely cespitose or not, long-rhizomatous. Culms solitary or not, erect, 50-130 cm. Leaves 4-7; basal sheaths brownish; sheath of distal leaf 3-21 cm; ligules rounded to triangular, 6-28 mm; blades 30-80 cm × 6-13 mm. Inflorescences 6-40 cm; peduncles of proximal spikes 1-13 cm, basal 2 peduncles 2-17 cm apart; of terminal spikes 1-12 cm, shorter than to somewhat exceeding the distal pistillate spike; bracts leafy, sheath 1-9 cm; blades 20-70 cm × 4-11 mm. Spikes: proximal pistillate spikes 2-6, the distal usually ± crowded, ascending, densely 8-90-flowered, usually cylindric, 2-8 × 1.5-3 cm; terminal staminate spikes 1-2, 2-10 cm × 2-5 mm. Pistillate scales 3-9 veined, lanceolate, 6-13 × 1.8-3.2 mm, apex acute to awned, awn rough, to 5.5 mm. Anthers 3, 3.5-7 mm. Perigynia ascending to spreading, strongly 17-25-veined, sessile, lance-ovoid, 12-18.5 × 3.8-6 mm, shiny, glabrous; beak conic, 6-9 mm. Achenes stipitate, rhombic, concave faces, angles thickened, prominently knobbed with hard, nipplelike points, 3-4.5 × (2.2-)2.4-3.4 mm; style same texture as achene. Fruiting late spring-summer. Wet forests, especially in openings around forest ponds, riverine wetlands, marshes, wet thickets; 0-500 m; Ont., Que.; Ark., Conn., Del., Fla., Ga., Ill., Ind., Iowa, La., Md., Mass., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tex., Vt., Va., W.Va., Wis. Carex lupuliformis is rare and local throughout much of its range, especially northward.
From Flora of Indiana (1940) by Charles C. Deam
Infrequent and local in swampy woods, wet ditches, and buttonbush swamps, and on borders of ponds.
Very much like no. 228 [Carex lupulina Willd.]; perigynia ascending to spreading; achene 3-4.5 נ2.4-3.4 mm, its faces strongly concave, diamond-shaped in outline, each lateral angle straight-tapering to each end from a hard, nipple-like knob near the middle; 2n=60. Wetter places than no. 228, in open marshes or along shores, sometimes in shallow water, or in very wet floodplain forests; Vt. and adj. Que. to Minn., s. to Va., Ky., and Tex.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.