Cyperus arenicola Steudel; C. fraternus Kunth; C. pseudovegetus Steudel var. arenicola (Steudel) Kükenthal; C. reflexus var. fraternus (Kunth) Kuntze

Herbs, perennial, cespitose; rhizomes elongate, scaly, 2–3 mm wide. Culms roundly trigonous to terete, 30–80 cm × 1–1.6 mm, glabrous. Leaves 1–6, 10–40 cm, glabrous or essentially so. Inflorescences: heads ovoid to pyramidal, 9–15 mm diam.; rays 0 or 3–6, 0.5–4 cm, glabrous; bracts 3–4, longest erect, appearing as continuation of culm, others horizontal to ascending, 4–17 cm × 1.5–4 mm. Spikelets 25–60, reddish with contrasting yellowish or greenish edges, oblong-lanceoloid, strongly compressed, 5–6(–15) × 1.5–2.5 mm; floral scales 10–22, laterally reddish, medially yellowish green, 2-keeled, laterally strongly 1-ribbed on each side, proximally grooved, ovate-elliptic, 1.4–2.2 × 0.8–1.5 mm, apex acute, apically scabridulous (sometimes glabrous). Flowers: stamen 1; anthers 0.6–1 mm; styles 0.3–0.5 mm; stigmas 0.3–0.6 mm. Achenes reddish brown, stipitate, ovoid-ellipsoid, 0.8–0.9 × 0.3–0.4 mm, stipe 0.1–0.2 mm, apex acute to acuminate, surfaces reticulate or subtly rugulose.

Fruiting late spring–fall (May–Oct). Muddy soils or shallow waters; 0–200 m; Fla., La., Okla., Tex.; Mexico; Central America (Costa Rica).

Cyperus reflexus is recognized by its reddish scales with contrasting greenish or yellow keels and by the laterally 1 ribbed scales. The lateral rib is most often situated where the reddish and yellowish parts of the scale meet. Two varieties of C. reflexus, var. reflexus and var. fraternus, have been recognized (M. F. Denton 1978b). Both varieties were noted as intermingled in the North American and South American segments of the widely disjunct range of C. reflexus. Such variation does not seem significant at the varietal level (see G. C. Tucker 1994; G. C. Tucker and R. McVaugh 1993).