6. Potamogeton crispus C. Linnaeus, Sp. pl. 1: 126. 1753 · Curled Pondweed
Rhizomes absent; cauline stems compressed, without dark spots, to 100 cm long. Turions present, common, terminal or axillary, 1.5–3 cm long, ca. 20 mm wide; outer leaves 1–4 per side, the base without corrugations, apex obtuse; inner leaves differentiated, rolled into hardened structure, parallel to outer leaves. Nodal glands absent. Leaves submersed, alternate, more or less spiraling. Submersed leaves sessile; ligules inconspicuous, free from blade, reddish brown, not fibrous, not shredding apically, deliquescent, convolute, to 0.5 cm long, the apex obtuse; leaf blade lax, light green to dark green, oblong, not arcuate, 1.2–9 cm long, 4–12 mm wide, with 3–5 veins, 2–5 rows of lacunae each side of midrib, the base parallel-sided to obtuse, nearly clasping, without basal lobes, the margins serrulate to serrate, the apex obtuse, not cucullate. Inflorescences unbranched, distal only; distal peduncles cylindrical, turgid, terminal or rarely axillary, erect to ascending, 2.5–7.5 cm long; spikes emersed, cylindrical, 7–15 mm long, the nodes 3–7, the internodes 0.3–3.5 mm long. Flowers alternate; perianth spathulate, clawed, the claw 0.4–0.8 mm long, the blade 1.3–1.6 mm long, 1.5–1.7 mm wide; anthers 0.7–1.2 mm long; carpels 4. Fruiting gynophore absent. Fruits obovate, red brown to red, turgid, abaxially rounded, laterally rounded, 2.5–6 mm long, 2–2.5 mm wide; beak apically recurved, 2.5–3 mm long; tubercules absent; embryo ca. one full spiral. 2n= 26 or 52.
Flowering spring--summer. Quiet waters, especially brackish, alkaline, or eutrophic waters, of ponds, lakes, and streams; 0--2000 m; introduced; Alta., B.C., Ont., Que.; Sask., Ala., Ariz., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Mich., Minn., Miss., Mo., Nebr., Nev., N.H., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Central America in Costa Rica; South America in Colombia and Argentina; Eurasia; Australia.
Potamogeton crispus is an introduced species that has spread throughout much of North America. Stuckey (1979) has discussed the expansion of this species’ range from its original collection in North America, which apparently was about 1840. This is the only species of pondweeds in North America with serrate leaves and, consequently, easily recognized.
Life history of Potamogeton crispus is unusual as it flowers and fruits in late spring and early summer, at which time it also produces turions. The plants decay shortly after these structures develop, leaving only fruits and turions, which survive the summer. No one has observed any seed germination, but Stuckey, Wehrmeister, and Bartolotta (1978) report that the turions (referred to as dormant apices) germinate in late summer or autumn, and the plants overwinter as small plants only a few cm in size, even under the ice in northern climates. Growth then continues as the water begins warming in the spring.
Selected references: Sastroutomo, S. S. 1981. Turion formation, dormancy and germination of curly pondweed, Potamogeton crispus L. Aquatic Bot. 10: 161--173. Stucky, R. L. 1979. Distributional history of Potamogton crispus (curly pondweed) in North America. Bartonia 46: 22--42. Stuckey, R. L., J. R. Wehrmeister, & R. J. Bartolotta. 1878. Submersed aquatic vascular plants in ice-covered ponds of central Ohio. Rhodora 80: 203--208.
One hybrid, Potamogeton crispus ´ P. praelongus = P. ´ undulatus J. F. Wolfgang ex F. A. Schultes & J. H. Schultes, has been described.
