Rhizomes absent. Cauline stems terete to slightly compressed, without spots, to 57 cm; glands white to gold, 0.2--0.3 mm diam. Turions: unknown. Leaves submersed, ± spirally arranged, sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, brown, not ligulate, to 0.62 cm, not fibrous, not shredding at tip, apex obtuse; blade green, linear, not arcuate, 3.2--7.8 cm ´ 0.7--1.7 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, lacunae rarely absent, in 0--4 rows each side of midrib; veins 3(--5). Inflorescences unbranched, emersed; peduncles not dimorphic, axillary or terminal, erect, cylindric, 3.2--4.8 cm; spike not dimorphic, capitate to cylindric, 5.5--7.5 mm. Fruits sessile, brown to yellow-green, obovoid, compressed, abaxially and laterally keeled, 2--2.2 ´ 1.7--1.8 mm, lateral keels without points; beak erect, 0.5--0.6 mm; sides with 1--3 tubercules near base; embryo with 1 full spiral.

Flowering and fruiting spring--summer. Small streams; of conservation concern; ca. 1800 m; Tex.

Potamogeton clystocarpus is an extremely limited species known from only one canyon in west Texas.