Class-book Bot. ed. s.n.(b), 734. 1861.
Herbs, perennial, single-stemmed to loosely cespitose. Culms basally cormlike, trigonous, (15–) 30–100 cm × 0.5–3.5 mm, glabrous. Leaves flat to V-shaped, 10–65 cm × 3–9 mm, adaxial surface, margins minutely scabridulous. Inflorescences: spikes densely globose to globose-ovoid, 8–17 mm wide; rays 3–12, 2–12 cm, scaberous adaxially especially distally; rachis 4–8 mm; bracts (3–) 4–7, ascending at 30 (–45) °, flat, 5–35 cm × 2–9 mm; rachilla persistent, wings 0.5–0.7 mm wide. Spikelets 50–100, oblong-lanceoloid, ± terete-quadrangular, (3.5–) 4–7 × 1–1.4 mm; distal spikelet spreading or ascending; floral scales persistent, 3–5, appressed, stramineous to brownish, 4-ribbed laterally, oblongelliptic, 3.5–4.5 × 1–1.8 mm, membranous, apex entire or emarginate with mucro to 0.3 mm. Flowers: anthers 0.4–0.8 mm; styles 0.5–0.6 mm; stigmas 1 mm. Achenes brown, ± stipitate, oblong, (1.5–) 1.8–2.3 × 0.5–0.6 (–0.7) mm (1/2 length of floral scales), apex obtuse, surfaces puncticulate.
Phenology: Fruiting summer–early fall.
Habitat: Disturbed, sunny sites, in mesic places, well-drained soils
Elevation: 0–500 m
Ala., Ark., Del., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va., Wis., West Indies
The records for Rhode Island and Wisconsin are according to M. L. Horvat (1941); we have not seen specimens from those states.
Cyperus echinatus is usually recognized by its tight, nearly spheric spikes; it may occasionally be hard to distinguish from C. croceus and C. retrorsus. Compared to C. retrorsus, C. echinatus has larger spikelets and longer floral scales, anthers, and achenes. In contrast to C. echinatus, C. croceus has looser spikes, shorter, broader, greenish or yellowish floral scales, shorter, more ovoid achenes, and shorter anthers. Furthermore, C. echinatus is predominantly an inland species of roadsides, pastures, and other disturbed ground; C. retrorsus is primarily a coastal species and occurs in drier, sandier sites.