36. Cyperus squarrosus Linnaeus, Cent. Pl. II. 6. 1756.
Chlorocyperus inflexus (Muhlenberg) Palla; Cyperus aristatus Rottbøll; C. aristatus var. inflexus (Muhlenberg) Kükenthal; C. aristatus var. runyonii O’Neill; C. inflexus Muhlenberg; Dichostylis aristata (Rottbøll) Palla; Mariscus squarrosus (Linnaeus) C. B. Clarke
Herbs, annual, cespitose, with fibrous roots. Culms 1–20, trigonous, 2–16 cm × 0.5–0.8 mm, glabrous. Leaves 1–3, flat to V-shaped, (1–)5–10(–15) × 0.5–2.5 mm. Inflorescences: spike 1, loosely to densely ovoid to oblong, 6–20(–40) × 9–15(–20) mm; rays absent or 1–3(–6), 4–40 mm; bracts (1–)2–4, longest ± erect, V-shaped, 1–15 cm × 0.5–3 mm; rachilla ± deciduous, wingless. Spikelets (2–)6–20(–40), greenish to reddish brown, somewhat compressed, ovoid-lanceoloid to oblong, 2.5–10(–20) × 1.3–2.2 mm (excluding awns); floral scales deciduous, (4–)10–20(–34), greenish to stramineous or brownish red laterally, greenish medially, (5–)7–9(–11)-ribbed nearly to margins, oblong-lanceolate, (1.2–)1.3–1.8(–2.2) × (0.5–)0.7–0.8(–1) mm, apex cuspidate, excurved awn additional 0.5–1(–1.3) mm. Flowers: stamen 1, filaments 1.5 mm; anthers oblong, 0.2–0.3 mm, connective apex reddish, minute; styles 0.3–0.5 mm; stigmas 0.4–0.7 mm. Achenes light brown to nearly black, stipitate, obovoid (occasionally linear-spatulate or linear oblong, infrequently constricted in middle), 0.7–0.8(–1.1) × (0.2–)0.3–0.4(–0.5) mm, stipe 0.05–0.1 × 0.1 mm, apex truncate, apiculate, surfaces papillose.
Fruiting summer. Moist, disturbed soils, gravelly roadsides, flood plains, edges of puddles, muddy places; 0–2500 m; Alta., B.C., Man., N.B., Ont., Que.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah., Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; West Indies; Bermuda; Central America; South America; Eurasia; Africa; Atlantic Islands; Indian Ocean Islands; Pacific Islands; Australia.
Cyperus squarrosus can be recognized by its small size and annual habit combined with its oblong-lanceolate floral scales bearing five to eleven conspicuous ribs and excurved awns. Some collections have been misidentified as C. acuminatus, an annual species of subg. Pycnostachys that has ovate-lanceolate, three-ribbed floral scales and digitately clustered spikelets.