Flora of North America species comparison

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Potamogeton pusillus subsp. gemmiparus

Potamogeton pusillus subsp. tenuissimus
Photo is of parent taxon

potamot gemmipare
Photo is of parent taxon

narrow-leaf small pondweed, potamot très ténu, small pondweed
Leaves

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.

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).
Inflorescences

peduncles 1–3 per plant, cylindric;

spikes cylindric, continuous.

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

spikes capitate to cylindric, continuous.
Fruits

obovoid, sides centrally concave;

beak median.

ovoid, sides rounded, rarely concave;

beak median, rarely toward adaxial edge.
2n

= 26.

Potamogeton pusillus subsp. gemmiparus

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

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.)

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.)
Source FNA vol. 22. FNA vol. 22.
Parent taxa Potamogetonaceae > Potamogeton > Potamogeton pusillus Potamogetonaceae > Potamogeton > Potamogeton pusillus
Sibling taxa
P. pusillus subsp. pusillus, P. pusillus subsp. tenuissimus
P. pusillus subsp. gemmiparus, P. pusillus subsp. pusillus
Synonyms P. pusillus var. gemmiparus, P. gemmiparus P. pusillus var. tenuissimus, P. berchtoldii, P. berchtoldii var. colpophilus, P. berchtoldii var. lacunatus, P. berchtoldii var. polyphyllus, P. berchtoldii var. tenuissimus
Name authority (J. W. Robbins) R. R. Haynes & Hellquist: Novon 6: 370. (1996) (Mertens & W. D. J. Koch) 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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