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Aquatic annual or rhizomatous perennial. Culms geniculately ascending, rooting at lower nodes, branching, succulent, 30–110 cm tall, upper nodes glabrous, often conspicuous. Leaves cauline; leaf sheaths striate, glabrous, lower sheaths often inflated; leaf blades linear, flat, 7–35 × 0.5–1 cm, glabrous, scabrid, base straight or subcordate, apex acute; ligule 1–2 mm, a ciliate membrane. Panicle terminal or axillary, pyramidal when fully exserted, 10–20 cm, much branched; branches glabrous, scabrid, secondary and tertiary branches often appressed. Spikelets lanceolate to narrowly ovate, 3–4 mm, glabrous, acuminate; lower glume broadly ovate, 1/6–1/3 length of spikelet, clasping at the base of the spikelet, membranous, 0–1-veined, obtuse to acute; upper glume as long as spikelet, 7–9-veined; lower lemma similar to upper glume, palea absent or present and well developed; upper floret 2/3 length of spikelet, green or pale yellow, smooth, shiny. Fl. and fr. Jun–Oct.
Glabrous annual to 1 m or more, erect to decumbent or diffuse; panicle in large plants to 4 dm, widely branched; lf-blades 4–20 mm wide; spikelets 1.6–3.3 mm, green or purple-tinged, ellipsoid to oblong; first glume broad, obtuse or rounded, a third as long; second glume and sterile lemma acute, 7-veined, the latter with or without a palea; 2n=36, 54. Moist soil and shores, often a weed in cult. land; N.S. and Que. to Minn. and S.D., s. to Fla. and Tex.
