Plants without conspicuous rhizomes. Culms 20-80 cm, 0.8-1.5 mm wide basally, 0.4-0.5 mm wide distally. Leaves: sheaths tight, green, fronts hyaline; ligules less than 2, wider than long; widest leaf blades 1.3-1.9 mm wide. Inflorescences with 4-8 spikes, 3-7 cm × 5-7.5 mm; proximal internodes more than 2 times as long as proximal spikes; proximal bracts to 5(-10) cm; spikes with 3-8 spreading or reflexed perigynia. Pistillate scales hyaline with green midvein, ovate, 1.4-2.3 × 0.9-1.6 mm, body 1/2 length of perigynium, apex obtuse, acute, or awned. Anthers 0.8-1.3 mm. Perigynia green, faces not veined, 2.6-3.8 × 1-1.5 mm, base of body spongy, thickened, longitudinally striate adaxially, spongy region 1-1.5 mm, margins serrulate distally; beak 0.4-1 mm, apical teeth 0.1-0.2 mm. Stigmas straight or slightly twisted, 0.03-0.06 mm wide. Achenes ovate to obovate, 1.5-2 × 1-1.4 mm. 2n = 58. Fruiting mid-late spring. Mesic to wet-mesic deciduous and mixed forests, often seasonally wet areas; 50-1000 m; Man., N.B., N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Vt., Va., W.Va., Wis. The name Carex rosea has frequently been misapplied to C. radiata.
Small Cespitose; stems 2-8 dm, erect, slender, the fertile ones 0.8-1.5 mm thick at base; lvs elongate, the widest ones 1.3-1.9 mm wide; spikes 4-7, androgynous, sessile, closely aggregated or the lower often distinctly separate; bracts setaceous, the lowest often surpassing the infl; pistillate scales persistent, shorter than the perigynia, rounded to acute, seldom short-awned; perigynia 3-20, light green, widely spreading or reflexed at maturity, planoconvex, lance-ovate, 2.6-3.8 mm, two-fifths as wide, spongy and somewhat swollen at the subtruncate or broadly rounded base, nerveless, or obscurely nerved near the base, gradually tapering or slightly acuminate into a serrulate, very shortly bidentate beak scarcely a third as long as the body; achene lenticular, ovate to obovate, 1.5-2 mm, occupying the upper half of the body of the perigynium, its base 0.5-0.9 mm above the base of the perigynium; stigmas very slender, straight to slightly twisted, only 0.03-0.06 mm wide; 2n=58. Moist woods and edges of ponds, requiring more moisture than the next 2 spp.; N.S. and s. Que. to Man. and N.D., s. to N.C., Ala., and Mo. (C. rosea, misapplied) The 2 following spp. are closely allied to C. radiata. The characters are confluent, but the populations apparently not.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.