American Journal of Science, and Arts 45:38. 1843.
Rhizomes present. Cauline stems terete, conspicuously spotted, 8–95 cm; nodal glands absent. Turions absent. Leaves both submersed and floating, ± spirally arranged. Submersed leaves petiolate, lax; stipules deliquescent, inconspicuous, convolute, free from blade, light to dark brown, not ligulate, 0.7–1.2 cm, not fibrous, not shredding at tip, apex obtuse; petioles 0.5–4.5 cm; blade dark green, linear-lanceolate to lanceolate, often arcuate, 3.5–13.8 cm × 60–165 mm acute, base acute to rounded, without basal lobes, margins entire, crispate, apex not hoodlike, acute to obtuse, lacunae in 2–5 rows each side of midrib; veins 7–19. Floating leaves: petioles continuous in color to apex, 1–16.5 cm; blade adaxially light to dark green, lanceolate to round-ovate, 2.5–8.5 cm × 11–44 mm, base rounded to cordate, apex acute to rounded; veins 15–21. Inflorescences unbranched, emersed; peduncles not dimorphic, terminal or axillary, erect to ascending, cylindric, 3.3–9.4 cm; spikes not dimorphic, cylindric, 17–36 mm. Fruits sessile, dark green to dark brown, ovoid to obovoid, turgid, abaxially keeled, laterally ridged, 5–6.5 × 4.1–5 mm, lateral ridges without points; beak erect, 0.5 mm; embryo with 1 full spiral. Chromosome number apparently unknown not available.
Phenology: Flowers summer–fall.
Habitat: Stagnant to slow-flowing waters of streams, lakes, ponds, and small rivers
Elevation: 0–700 m
N.B., N.S., Ont., P.E.I., Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va., Wis.
Potamogeton pulcher is similar in morphology to P. amplifolius and occurs in similar habitats. Potamogeton pulcher differs from P. amplifolius by the former having lanceolate to linear-lanceolate submersed leaves with fewer than 19 veins, whereas the latter has ovate submersed leaves with more than 19 veins.