Cyperus uniflorus Torrey & Hooker var. pseudothyrsiflorus Kükenthal in H. G. A. Engler, Pflanzenr. 101[IV,20]: 521. 1936

Herbs, perennial, cespitose, rhizomatous. Culms trigonous, base thickened, tuberous, 15–40 cm × 2–2.6 mm, glabrous. Leaves flat to V-shaped, 10–30 cm × (3–)4–5.8 mm. Inflorescences: spike 1, densely oblong to ellipsoid, 10–20 × 10–20 mm; rays 4–12, 10–20 cm bracts 3–6, horizontal to ascending at 30°, V-shaped, 3–15 cm × (3–)4–5.8) mm; rachilla deciduous, wings persistent, 0.5–0.7 mm wide. Spikelets (5–)10–20(–30), linear to oblong, quadrangular, (2.2–)4–12(–16) × 0.7–1.2 mm, densly packed on rachis with 11–21 spikelets per 5 mm rachis; distal spikelet spreading or ascending; floral scales persistent, 1–5, appressed, laterally whitish to reddish brown, medially green, narrowly oblong to ovate, laterally 3–6-ribbed, 2.4–3.4 × 1.6–2 mm, apex rounded to ± acute, entire, mucronate, mucro 0.1–0.3 mm; sterile terminal scale, involute, only 0.4–0.6 mm wide with mucro 0.2–0.5 mm. Flowers: anthers (0.3–)0.4–0.7 mm; styles 0.4–0.5 mm; stigmas 0.5–0.9 mm. Achenes light brown, sessile to slightly stipitate, ellipsoid to narrowly ellipsoid to narrowly obovoid, 1.4–1.9 × 0.5–0.75 mm, apex slightly apiculate, surfaces puncticulate.

Fruiting mid summer–early fall (Jul–Sep). Damp, disturbed soils, croplands; 0–1000 m; Tex.; Mexico.