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.
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.