Plants annual; rhizomes absent; roots reddish, fibrous. Culms solitary or in tufts, erect, slender, (7–) 10–60 cm, glabrous. Leaves: sheaths green or streaked with purple, smooth or weakly ribbed, usually narrowly winged, long-villous; contra-ligules minute; blades linear or filiform, plane or keeled, shorter than culms, 0.5–2 mm wide, glabrous. Inflorescences terminal, glomerate-spicate, 2.5–13 cm; glomerules 2–9, erect, brown, compact, 3–7 mm wide, each with 5–12(–15) spikelets; proximal glomerules occasionally on short, erect peduncles; rachis glabrous; bracts subtending inflorescence bristlelike, minutely ciliate or glabrous, inconspicuous. Spikelets bisexual, alternate, often appearing cyclic or whorled, 2–3(–4) mm; scales oblong-lanceolate. Achenes whitish or often gray or brownish or with dark interangular markings, trigonous-globose, 1–1.5(–1.9) mm, base trigonous, stipelike, short, narrowly constricted, and somewhat pitted or ribbed, apex distinctly mucronate, surface transversely tuberculate with quadrate ridges; hypogynium obsolete, represented by narrow brownish ridge at base of achene.
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Annual; very slender, 2–6 dm, often tufted; sheaths usually long-villous; main blades 1 mm wide; infl of 2–8 short, capitate cymes each 2–4 mm, sessile, subtended by inconspicuous bracts 4–7 mm, forming an erect interrupted spike; anthers 1 mm; scales glabrous, lanceolate, keeled; achene white, subglobose, 1 mm thick, conspicuously apiculate, verrucose or transversely ridged, constricted below to a short smooth hypogynium. Wet sandy soil; widespread in trop. Amer., n. to Conn. and Minn.
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