Flora of North America species comparison

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Potamogeton pusillus subsp. tenuissimus

Potamogeton pusillus subsp. gemmiparus
Photo is of parent taxon

narrow-leaf small pondweed, potamot très ténu, small pondweed
Photo is of parent taxon

potamot gemmipare
Leaves

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).

stipules convolute;

blade 1.1–6 cm × 0.2–0.7 mm, apex subulate, lacunae present or absent, 0–2 rows on each side of midrib;

veins 1.
Inflorescences

peduncles more than 3 per plant, cylindric to slightly clavate;

spikes capitate to cylindric, continuous.

peduncles 1–3 per plant, cylindric;

spikes cylindric, continuous.
Fruits

ovoid, sides rounded, rarely concave;

beak median, rarely toward adaxial edge.

obovoid, sides centrally concave;

beak median.
2n

= 26.

Potamogeton pusillus subsp. tenuissimus

Potamogeton pusillus subsp. gemmiparus
Phenology Flowering and fruiting summer–fall. Flowering and fruiting summer–fall.
Habitat Shallow waters of lakes and streams Acid waters of lakes and streams
Elevation 0–2100 m (0–6900 ft) 0–100 m (0–300 ft)
Distribution
from FNA
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
from FNA
CT; MA; ME; NH; NH; VT; QC
Discussion

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.)

Potamogeton pusillus subsp. gemmiparus is an uncommon taxon that superficially resembles subsp. pusillus. It can be separated, however, by its continuous inflorescences, whereas those of subsp. pusillus are interrupted.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 22. FNA vol. 22.
Parent taxa Potamogetonaceae > Potamogeton > Potamogeton pusillus Potamogetonaceae > Potamogeton > Potamogeton pusillus
Sibling taxa
P. pusillus subsp. gemmiparus, P. pusillus subsp. pusillus
P. pusillus subsp. pusillus, P. pusillus subsp. tenuissimus
Synonyms P. pusillus var. tenuissimus, P. berchtoldii, P. berchtoldii var. colpophilus, P. berchtoldii var. lacunatus, P. berchtoldii var. polyphyllus, P. berchtoldii var. tenuissimus P. pusillus var. gemmiparus, P. gemmiparus
Name authority (Mertens & W. D. J. Koch) R. R. Haynes & Hellquist: Novon 6: 370. (1996) (J. W. Robbins) R. R. Haynes & Hellquist: Novon 6: 370. (1996)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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