Rhizomes present. Cauline stems compressed, without spots, 5--40 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 for ½ stipule length, reddish brown to light green, ligulate, 2--12 mm, not fibrous, not shredding at tip, apex obtuse; blade red-brown to light green, linear, not arcuate, 0.8--8 cm ´ 0.5--2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse to acute, lacunae present, a broad band each side of midvein; veins 1--3. Floating leaves petiolate; petioles continuous in color to apex, 5--25 mm; blade adaxially light green, oblong to obovate, 0.7--—3.5 cm ´ 2--13 mm, base tapered to rounded, apex obtuse, rounded; veins 5--15. Inflorescences unbranched; peduncles dimorphic, submersed axillary, recurved, clavate, 0.5--3 mm, emersed axillary or terminal, erect to recurved, slightly clavate, 4--27 mm; spikes dimorphic, submersed capitate, 2--5 mm, emersed ellipsoid to cylindric, 4--13 mm. Fruits sessile, greenish brown, somewhat orbicular, compressed, abaxially winged, laterally winged, 4--13 ´ 1.3--2.4 mm, lateral wing with blunt tips; beak absent; sides without basal tubercles; embryo with more than 1 full spiral.
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Much like no. 17 [Potamogeton diversifolius Raf.]; submersed lvs 1–8 cm × 0.5–2 mm, mostly 15–80 times as long as wide, rounded or obtuse to sometimes acutish at the tip, 1-or 3-veined, usually with 2 or 3 rows of lacunar cells flanking the midvein; adnate part of the stipular sheath longer than the free part; floating lvs (not always produced) 7–35 × 2–13 mm, with 5–13 veins; submersed spikes globular, with 1–8 frs, on recurved peduncles to 3 mm, the aerial ones more cylindric, to 13 mm, with 4–35 frs; fr 1.3–2.4 mm, with a sharp, entire to sinuate dorsal keel, the smooth sides conforming to the embryo. Shallow water; Nf. to Que. and sw. Ont., s. to Va., n. O., and n. Io. (P. dimorphus, misapplied)
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