27. Potamogeton nodosus Poiret in J. Lamarck et al., Encyclopedie Methodique. Botanique ... Supplement. 4(2): 5354. 1816.
Long-leaf pondweed, potamot noeuex
Rhizomes present. Cauline stems terete, without spots, to 100 cm; nodal glands absent. Turions absent. Leaves both submersed and floating, or floating absent, ± spirally arranged. Submersed leaves petiolate, lax; stipules persistent to deliquescent, conspicuous, convolute, free from blade, light brown, not ligulate, 3--9 cm, not fibrous, not shredding at tip, apex round to acute; petioles 2--13 cm; blade light to dark green, linear-lanceolate to lance-elliptic, not arcuate, 9--20 cm ´ 10--35 mm, base acute, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, without sharp awl-like tip, lacunae in 2--5 rows each side of midrib; veins 7--15. Floating leaves: petioles 3.5--26 cm; blade adaxially light green, lenticular to elliptic, 3--11 cm ´ 15--45 mm, base cuneate to rounded, apex acute to rounded; veins 9--21. Inflorescences unbranched, emersed; peduncles not dimorphic, terminal, erect to ascending, cylindric, 3--15 cm; spikes not dimorphic, cylindric, 20--70 mm. Fruits sessile, red to reddish brown, obovoid, abaxially keeled, laterally ridged, 2.7--4.3 ´ 2.5--3 mm, keel well developed, lateral ridges with blunt to sharp tips; beak erect; sides without basal tubercles; embryo with 1 full spiral. 2n = 52.
Flowering summer--fall. Clear to turbid waters of lakes, streams, rivers, and sloughs; 0--3300 m; Alta., B.C., N.B., Ont., Que., Sask.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; West Indies; Central America; South America; Eurasia.
Six hybrids, Potamogeton gramineus ´ P. nodosus (= P. ´ argutulus Hagström), P. illinoensis ´ P. nodosus (= P. ´ faxonii Morong), P. nodosus ´ P. richardsonii (= P. ´ rectifolius A. Bennett), P. natans ´ P. nodosus (= P. ´ schreberi Fischer [P. ´ perplexus A. Bennett]), P. alpinus ´ P. nodosus (= P. ´ subotusus Hagström), and P. epihydrus ´ P. nodosus (= P. ´ subsessilis Hagström), have been described.
Potamogeton nodosus is a common floating-leaved species throughout much of the United States and southern Canada. When both submersed and floating leaves are present, it is very easily recognized by the petioles of the submersed leaves being longer than 5 cm.