Plants annual, cespitose, 15–50(–70) cm, glabrous, base soft; rhizomes absent. Leaves distichous, in fans, to ca. 2/3 plant height; sheaths keeled, equitant, margins entire; ligule absent; blades bifacial (flattened in same plane as sheath), narrowly triangular linear, to 2 mm wide, margins scabrid at least distally. Inflorescences: anthela compound, usually diffuse, branched, broadening upward, often as broad as long; scapes slender, angularly ribbed and/or somewhat compressed distally, 1–1.5 mm wide or thick; involucral bracts exceeded by anthela. Spikelets dark red-brown, broadly ovoid to near round, 2–4 min; fertile scales broadly ovate to orbiculate, 1 mm, glabrous, apex broadly rounded, midrib not excurrent. Flowers: stamens 1–2; styles 3-fid, slender, base dilated, apex pubescent. Achenes pale brown, tumid, obovoid, 1 mm, apiculate, reticulate, with pits narrowly rectangular in 4–6 vertical rows per side, the longitudinal ribs most prominent and mostly warty. 2n = 10.
Annual, slender, glabrous, 2-7 dm. high; leaves soft, 1-3 mm. wide, usually shorter than the culms; spikelets numerous, subglobose, 2-4 mm. long, brown, in a decompound inflorescence; achenes trigonous, minute (0.5 mm. long), pale brown, frequently iridescent.
Tufted, glabrous annual, 10-40 cm. Stem 0.8-1.2 mm diam., usually triangular or quadrangular, sometimes compressed, sides deeply concave. Leaves as long as stem or longer; lower sheaths open, prominently nerved, with widely scarious margins, upper 2(-3) closed, 2-8 cm, mouth oblique, one side green, many-nerved, nerves ending in acute apex, mouth margin scarious; blades 1.5-2 mm wide, laterally compressed, adaxial side narrow groove at one "margin", margins towards apex slightly barbed. Inflorescence up to 50 mm diam., taller than wide, with 15-50 spikes; bracts up to 20 mm, involute; branches triangular or compressed, much longer than spikes, smooth or distal parts barbed. Spikes 1.5-3 mm, pedunculate or sessile, globular or ellipsoid, obtuse, pale yellow to brown, with from few to more than 30 glumes; spike rachis castaneous to almost black, with narrow hyaline wings; glumes 1-1.2 mm, cymbiform, ovate, keeled, apiculate or sometimes obtuse, brown to almost hyaline. Stamens 1-2, anthers c. 1 x 0.3 mm, mucronate; style 0.3-0.4 mm, brown, base mostly bulbous, deciduous; stigmas (2-)3. Nut 0.5-0.6 x 0.3-0.4 mm, globular to obovoid, faintly trabeculate, papillose, grey to pale yellowish or white.
Annual or short-lived perennial. Culms arising from leaf axils, several, 10–60(–90) cm by 1–3 mm, 4-sided, smooth. Leaves basal, or cauline reduced to bladeless sheaths; blade linear, 10–50 cm by 1–4 mm, subacute, bilaterally flattened; basal sheaths 1–18 cm long, open, cauline sheaths tubular, 2–10 cm long; ligule 0. Involucral bracts 2–4, setaceous, the longest 1–3 cm long. Inflorescence compound to decompound, open, 3–10 by 3–10 cm; primary branches 3–7, 1–7 cm long. Spikelets many per inflorescence, ovoid-globose to globose, 1.5–3(–5) by 1–2.1 mm. Glumes many per spikelet, spirally arranged, broadly ovate, 1–1.2 by 0.6–0.8 mm, obtuse, sides membranous, reddish brown, margins broadly hyaline, keel obtuse, yellowish, obscurely 3-nerved. Stamens 1(–2); anthers 0.6 mm long. Stigmas 3. Nutlets obovoid, trigonous, 0.6–0.8 by 0.3–0.5 mm, creamy yellow, sparsely verruculose especially on angles, cancellate with 5–7 longitudinal rows of transversely linear-oblong cells.
Tufted annual to 5(–10) dm; lvs distichous and equitant, smooth, rigid; ligule wanting; longest invol bract shorter than the infl; spikelets 2–4 mm, stout, in a loose to congested system of cymes; scales ovate, usually blunt or emarginate; stamens 1 or 2; anthers less than 1 mm; style trifid, not much longer than the achene, ± fimbriate below the branches; achene 1 mm, obovoid, plump but scarcely trigonous, with several smooth or often warty vertical ribs connected by numerous fine raised ridges; 2n=10. Wet places, often a rice-field weed; pantropical, n. to Ky.