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Plants perennial, in fresh water, usually with reddish tinge particularly when dry. Rhizome slender. Stems terete, 1.5-2 mm in diam., simple, but sometimes with horizontal stolons. Leaves dimorphic; stipules axillary, convolute, herbaceous, slightly amplexicaul, 12-35 mm. Submerged leaves sessile, lanceolate to linear-lanceolate or elliptic-oblong, 5-38 × 0.7-3.3 cm, 9-19-veined, with broad rows of lacunae bordering midvein, base cuneate, margin entire, apex obtuse. Floating leaves petiolate; blade elliptic to broadly lanceolate, 4-9 cm × 8-25 mm, leathery or subleathery, (5-)7-13-veined, base cuneate to narrowly cuneate, margin entire, apex obtuse. Spikes cylindric, 6-15 cm, densely flowered; peduncles thicker than stem. Carpels 4. Fruit obovoid, 2.6-3.7 mm, abaxial keel somewhat sharp, with a short beak. Fl. and fr. Jul-Sep. 2n = 52.
Stem slender, somewhat flattened, often branched, to 2 m; rhizomes elongate; lvs sessile, linear, to 2 dm, 2–10 mm wide, 5–13-nerved, the midrib flanked by a pair ofconspicuous bands (each 1–2+ mm wide) of pale green or translucent lacunar cells; stipules 1–3 cm, free; floating lvs usually numerous, linear-elliptic to somewhat spatulate or narrowly obovate, 3–7 cm × 8–20 mm, 11–27-veined, mostly obtuse, narrowed below to a slender petiole about as long as the blade; peduncles about as thick as the stem, 2–5 cm, seldom longer; spikes numerous, cylindric, dense, 1–3 cm; frs obliquely obovoid, 2.5–4 mm, shallowly pitted, the sharp dorsal keel flanked by a pair of lower ones; 2n=26. Ponds and slow streams; Nf. to Que. to s. Alas., s. to Ga., La., and Calif.
