Potamogeton pusillus L.

Three hybrids, Potamogeton perfoliatus ´ P. pusillus (= P. ´ mysticus Morong), P. friesii ´ P. pusillus (= P. ´ pusilliformis Fisher [P. ´ intermedius Fischer]), and P. obtusifolius ´ P. pusillus (= P. ´ saxonicus Hagström), have been described.

Aquatic, perennating with axillary winter-buds. Stem filiform, c. (0.5-) 1 mm broad, branched. Leaves submerged, sessile, linear, 1-2 mm broad, tip tapering or rounded, 3(-5)-veined, midrib without lacunae. Stipules free, 6-8 mm long, 2 mm broad, ovate, acute, entire, membranous, tubular towards the base. Peduncles 1.2-3 cm long; spikes 5 mm long, few flowered, with 2-4, distant whorls. Perianth segments 1-1.5 mm long, 1-2 mm broad, broadly obtuse. Fruitlets c. 2 mm long, 1-1.5 mm broad, obovoid.

Rhizomes absent. Cauline stems terete to slightly compressed, without spots, 18--150 cm; glands present on at least some nodes, green, gold, brown, or rarely white, to 0.5 mm diam. Turions common, soft, lateral or terminal, 0.9--3.2 cm ´ 0.3--1.8 mm, soft; leaves ± 2-ranked; outer leaves 1--3 per side, base not corrugate, apex subulate to obtuse; inner leaves rolled into hardened fusiform structure. Leaves submersed, ± spirally arranged, sessile, delicate to coarse; stipules persistent, inconspicuous, connate or convolute, free from base of blade, brown to green or white, not ligulate, 0.31--0.92 cm, rarely appearing fibrous, not shredding at tip, apex obtuse; blade pale green to olive-green, rarely somewhat reddish, linear, not arcuate, 0.9--6.5 cm ´ 0.2--2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, subulate to obtuse, lacunae absent or present, in 0--5 rows each side of midrib; veins 1--3(--5). Inflorescences unbranched, submersed or emersed; peduncles not dimorphic, axillary or terminal, erect, rarely recurved, filiform to slightly clavate, 0.5--6.2(--6.6) cm; spikes not dimorphic, capitate to cylindric, 1.5--10.1 mm. Fruits sessile, green to brown, ovoid to obovoid, turgid to concave, not abaxially or laterally keeled, 1.5--2.2 ´ 1.2--1.6 mm; beak erect, 0.1--0.6; sides without basal tubercles; embryo with less than 1 full spiral.

Europe, Afriea, temperate Asia, N. Ameriea.

Distribution: Europe, temperate Asia, Africa and N. America.

2100-3000 m

Fl. Per.: June July.