Plants with basal sheaths of previous year not persistent. Culms easily compressed, to 120 cm × 7 mm, scabrous. Leaves: sheaths usually all with blades, green; fronts rugose, indistinctly linearly veined, apex colorless, fragile, convex, not forming extension, erose; ligules acute, 10 mm, free limb to 0.8 mm; blades not epistomic, to 100 cm × 15 mm. Inflorescences densely spicate, elongate, cylindric, with 15-25 distinguishable branches, 5-15 × 4 cm; proximal internode to 10 mm. Scales hyaline. Perigynia pale brown with red-brown veins, 15-veined abaxially, 7-veined adaxially, to 6 × 2 mm, base distended proximally, cordate; stipe to 0.4 mm; beak to 3.5 mm, serrulate. Achenes ovate, to 2 × 1.5 mm; stalk to 0.3 mm; persistent style base cylindric.
Stems stout, triangular, densely clustered, 3-10 dm; lvs coarse and often elongate; sheaths prolonged beyond the base of the blade, ventrally thin, fragile, and ±conspicuously cross-corrugated; spikes numerous, androgynous, small, few-fld, sessile, closely aggregated into a dense, compound infl 3-10 נ1-3 cm; bracts short and inconspicuous, or some of them setaceous and surpassing the spikes; scales mostly shorter than the perigynia, these greenish or greenish-stramineous, widely spreading (the infl appearing prickly because of the prominent beaks), lance-triangular or lance-ovate, gradually narrowed from the base to the tip, or a little more abruptly so near the middle, planoconvex, spongy-thickened at the base, prominently nerved-striate on both sides or seldom nerveless ventrally; achene lenticular; 2n=48, 52. Wet low ground; Nf. to Alas., s. to Fla., N.M., and Calif. Var. stipata, the common phase in our range, extending s. to N.C. and Tenn., has the main blades mostly 5-10 mm wide, the scales acuminate or merely cuspidate, the perigynia 4-5.2 (avg 4.7) mm and a third as wide. Var. maxima Chapm., the Gulf states phase, extending n. on the coastal plain to s. N.J. and inland to Mo. and Ind., is stouter, with larger and thicker heads and stems, the main blades 8-15 mm wide, the scales cuspidate or short-awned, the perigynia 5-6 (avg 5.4) mm and less than a third as wide, due to the relatively longer beak. (C. uberior)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.