Plants densely to loosely cespitose; rhizomes short, no more than 10 cm. Culms trigonous in cross section, 50-120 cm, scabrous distally. Leaves: basal sheaths pale brown; ligules usually much longer than wide; blades mid to dark green, flat to W-shaped, 5-16 mm wide, glabrous. Inflorescences 4-35 cm; proximal bract 15-85 cm, much longer than inflorescence; proximal (2-)3-6 spikes pistillate, erect or the proximal pendent, cylindric, 12-18 mm thick; terminal staminate or, sometimes, gynaecandrous, androgynous, or mixed. Pistillate scales lanceolate-acuminate, 2.8-12 × 0.4-1 mm, all but the proximal shorter than perigynia, margins ciliate, apex tapering to long scabrous awn. Staminate scales scabrous-awned, sometimes ciliate-margined. Perigynia spreading to reflexed when mature, strongly 14-22-veined, most veins separated by less than 2 times their width, confluent at or proximal to mid beak, tightly investing achene, narrowly elliptic to lanceolate, (4.8-)6.2-8.7 × 1.1-1.8 mm, leathery, apex gradually tapered; beak poorly defined, 2-3.8 mm, bidentate, teeth outcurved, 1.3-2.1(-2.8) mm. Stigmas 3. Achenes pale brown, trigonous, smooth. Fruiting Apr-Jul. Swamps and wet thickets, stream, pond, and lakeshores, depressions in wet meadows, marshes, including freshwater tidal marshes; often in shallow water or on emergent stumps, floating logs, and floating mats of vegetation; 0-700 m; Ont., Que.; Ark., Calif., Conn., Del., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Miss., N.J., N.Y., N.C, Ohio, Pa., S.C., Tenn., Tex., Vt., Va., Wis.; Mexico. Carex comosa is uncommon and local in the west and south of glaciated regions in the east except in some coastal areas. Carex comosa rarely forms sterile hybrids with C. pseudocyperus and C. hystericina.
From Flora of Indiana (1940) by Charles C. Deam
Fairly common in northern Indiana on low borders of lakes (often in shallow water) and in swamps, sloughs, and ditches. In southern Indiana it is known only from a single collection from Floyd County.
Much like no. 200 [Carex hystericina Willd.]; stems stout; lowest bract surpassing and sometimes several times as long as the infl; terminal spike to 6 cm, staminate or sometimes androgynous or gynaecandrous or with the perigynia in the middle; pistillate spikes 2-7, loose and ±nodding on slender peduncles, tending to be rather closely grouped together; perigynia ±reflexed, firm-textured and only slightly or scarcely inflated, obtusely trigonous, tapering to a short-stipitate base, and very gradually tapering above to the long beak with slender, firm, arcuate or divergent teeth 1.2-2.3 mm; mature style straight or seldom flexuous or contorted. Swamps and wet meadows; Que. to Minn., s. to Fla. and La.; Wash. to Calif. and n. Ida.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.