Rhizomes present. Cauline stems compressed, without spots, 10--35 cm; glands absent. Turions absent. Leaves both submersed and floating or floating absent, ± spirally arranged. Submersed leaves sessile, lax; stipules persistent to deliquescent, inconspicuous, convolute, adnate to blade ½ stipule length, light brown to red-brown, ligulate, 1.5--2.3 cm, not fibrous, not shredding at tip, apex obtuse; blade red-brown to light green, linear, often arcuate, 1--1.3 cm ´ 0.1 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, lacunae present, 1--2 rows each side midrib; veins 1. Floating leaves petiolate; petioles continuous in color to apex, 0.7--0.8 cm; blade adaxially light green, obovate to elliptic, 0.8--1.6 cm ´ 3--8.5 mm, base acute, apex round to acute; veins 3--7. Inflorescences unbranched; peduncles dimorphic, submersed axillary, recurved, clavate, 3--5 mm, emersed axillary or terminal, erect to slightly recurved, clavate, 6--15 mm; spikes dimorphic, submersed capitate, 2--3 mm, emersed cylindric, 5--9.7 mm. Fruits sessile, greenish brown, orbicular, compressed, abaxially winged, laterally winged, 1--1.5 ´ 0.9--2 mm, lateral wings with sharp points; beak present, erect, 0.1 mm; sides without basal tubercles; embryo with more than 1 full spiral.
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Stems slender, to 15 dm, clustered, sparsely branched above the base; submersed lvs linear to filiform, 1–10 cm × 0.1–0.5 mm, obtuse to more often acute or even setaceous-tipped, 1(3)-veined, the larger ones with narrow lacunar bands flanking the midvein; stipular sheaths membranous, 2–18 mm, the adnate part mostly shorter than the free tip; floating lvs (not always produced) lance-elliptic to suborbicular, acute to rounded at each end, 5–40 × 2–20 mm, the 3–17 veins strongly impressed beneath, their stipular sheath free from the 5–40 mm petiole; fruiting spikes dimorphic, those axillary to submersed lvs globular to ellipsoid, with 1–15 frs, on ± recurved, slightly clavate peduncles 1–10 mm, those axillary to floating lvs more cylindric, sometimes to 3 cm, with 5–120 frs, on peduncles 3–32 mm; frs compressed, ± orbicular, 1–2 mm, with a minute beak, the entire or toothed dorsal keel usually flanked by a pair of lateral keels that may be represented only by a row of teeth; embryo snail-coiled. Shallow water; Me. to Mont. and Oreg., s. to Fla. and Mex. Two fairly well marked vars.
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