Potamogeton pusillus |
Potamogeton pusillus subsp. tenuissimus |
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small pondweed |
narrow-leaf small pondweed, potamot très ténu, small pondweed |
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Rhizomes | absent. |
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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. |
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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. |
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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). |
stipules convolute; blade 0.9–5.4 cm × 0.2–2.5 mm; apex acute to obtuse, lacunae in 1–5 rows each side of midrib; veins 1–3(–5). |
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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. |
peduncles more than 3 per plant, cylindric to slightly clavate; spikes capitate to cylindric, continuous. |
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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. |
ovoid, sides rounded, rarely concave; beak median, rarely toward adaxial edge. |
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2n | = 26. |
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Potamogeton pusillus |
Potamogeton pusillus subsp. tenuissimus |
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Phenology | Flowering and fruiting summer–fall. | |||||||||
Habitat | Shallow waters of lakes and streams | |||||||||
Elevation | 0–2100 m [0–6900 ft] | |||||||||
Distribution |
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NS; NT; NU; ON; PE; QC; SK; YT; nearly worldwide
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AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KY; LA; MA; MD; ME; MI; MN; MS; MT; NC; ND; NH; NJ; NV; NY; OH; OK; OR; PA; RI; SC; VA; VT; WA; WI; WY; AB; BC; MB; NB; NL; NS; NT; NU; ON; PE; QC; SK; YT; Eurasia |
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Discussion | 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. Subspecies 3 (3 in the flora). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Although Delaware and West Virginia lies within the mapped area, we know of no collections from that state. Potamogeton pusillus subsp. tenuissimus is the most common linear-leaved subspecies of the family in temperate North America. Whenever one finds a linear-leaved pondweed with 1–5 rows of lacunae on each side of the midvein, chances are that it is subsp. tenuissimus. Only Potamogeton obtusifolius could be confused with the taxon, and it can be separated by having its cylindric inflorescence, whereas subsp. tenuissimus has a capitate inflorescence. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 22. | FNA vol. 22. | ||||||||
Parent taxa | ||||||||||
Sibling taxa | ||||||||||
Subordinate taxa | ||||||||||
Synonyms | P. pusillus var. tenuissimus, P. berchtoldii, P. berchtoldii var. colpophilus, P. berchtoldii var. lacunatus, P. berchtoldii var. polyphyllus, P. berchtoldii var. tenuissimus | |||||||||
Name authority | Linnaeus: Sp. Pl. 1: 127. 1753 (as pusillum) | (Mertens & W. D. J. Koch) R. R. Haynes & Hellquist: Novon 6: 370. (1996) | ||||||||
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