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FNA | Family List | FNA Vol. 22 | Potamogetonaceae | Potamogeton

16. Potamogeton pusillus Linnaeus, Sp. Pl. 1: 127. 1753 (as pusillum).

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.

Subspecies 3 (3 in the flora): nearly worldwide.

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.

1 Leaf blade 1-veined, subulate, 0.2--0.7 mm wide; New England and s Quebec .   16c subsp. gemmiparus
+ Leaf blade 1--5-veined, acute to obtuse, 0.2--2.5 mm wide; widespread throughout North America.   (2)
2 (1) Mature fruits obovoid, sides concave; beak toward adaxial edge, rarely median; peduncles filiform to cylindric, 1--3 per plant; inflorescences interrupted; leaf blade with 0--2 rows of lacunae along midrib, apex acute, rarely apiculate, rarely with bristle; stipules connate.   16a subsp. pusillus
+ Mature fruits widest at middle or ovoid, sides rounded; beak median, not toward adaxial edge; peduncles cylindric, more than 3 per plant; inflorescences continuous; leaf blade with 1--5 rows of lacunae along midrib, apex acute to obtuse; stipules convolute.   16b subsp. tenuissimus

Lower Taxa


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