18. Potamogeton foliosus Rafinesque, Medical Repository. hexade 2, 5:354. 1808.
Rhizomes absent. Cauline stems slightly compressed, without spots, 4--75 cm; glands rarely present, black to gold, to 0.5 mm diam. Turions uncommon, lateral or terminal, 0.9--2.5 cm ´ 0.6--2 mm, soft; outer leaves 1--3 per side, base not corrugate, apex acute to apiculate; inner leaves rolled into hardened fusiform structure. Leaves submersed, ± spirally arranged, sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, greenish to brown or rarely white, not ligulate, 0.2--2.2 cm, delicate to fibrous, rarely shredding at tip, apex obtuse; blade pale green to olive-green, rarely somewhat reddish, linear, not arcuate, 1.3--8.2 cm ´ 0.3--2.3 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, rarely with bristle, lacunae rarely present, 0--2 rows each side of midrib; veins 1--3(--5). Inflorescences unbranched, emersed; peduncles not dimorphic, in axils of proximal, rarely distal leaves, recurved, clavate, 0.3--1.1(--3.7) cm; spikes not dimorphic, capitate to cylindric, 1.5--7 mm. Fruits pale green to olive-green or brown, obovate to nearly orbicular, turgid to concave, sessile, abaxially keeled, not laterally keeled, 1.4--2.7 ´ 1.1--2.2 mm, abaxial keel undulate, winglike; beak erect, 0.2--0.6 mm; sides without basal tubercles; embryo with 1 full spiral.
Subspecies 2 (2 in the flora): North America, Central America.
