Potamogeton pusillus |
Potamogeton bicupulatus |
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small pondweed |
snail-seed pondweed |
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Rhizomes | absent. |
present. |
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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. |
compressed, without spots, 10–25 cm; glands absent. |
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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. |
absent. |
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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). |
both submersed and floating or floating absent, ± spirally arranged. |
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Floating leaves | petiolate; petioles continuous in color to apex, 5–35 mm; blade adaxially light green, lanceolate-elliptic to broadly elliptic, 0.6–2.3(–2.8) cm × 1–11 mm, base tapering or rounded, apex acute to long tapering; veins 3–7. |
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Submersed leaves | sessile, lax; stipules persistent to deliquescent, inconspicuous, convolute, adnate to blade for less than ½ stipule length, light green, ligulate, 0.2–1.2 cm, not fibrous, not shredding at tip, apex obtuse; blade light green to rarely brown, linear-setaceous, not arcuate, 1.5–11 cm × 0.1–0.4(–0.6) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, tapering, lacunae absent; veins 1. |
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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. |
unbranched; peduncles dimorphic, submersed axillary, somewhat recurved, clavate, 1–10 mm, emersed axillary or terminal, erect to slightly recurved, slightly clavate, 3.5–22 mm; spikes dimorphic, submersed, globular to ellipsoid, 1.5–7 mm, emersed ellipsoid to cylindric, 3–14 mm. |
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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. |
sessile, greenish brown, somewhat orbicular, compressed, abaxially keeled, laterally keeled, 1.1–2.1 × 1.1–2 mm, lateral keel without points; beak absent; sides without basal tubercles; embryo with more than 1 full spiral. |
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Potamogeton pusillus |
Potamogeton bicupulatus |
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Phenology | Flowering early summer–fall. | |||||||||
Habitat | Acidic waters of ponds, lakes, and streams | |||||||||
Elevation | 0–300 m [0–1000 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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CT; DE; IN; MA; ME; MI; NH; NY; PA; RI; TN; VA; VT; WI; ON
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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.) |
Potamogeton bicupulatus is an uncommon species of the acid lakes and streams of northeastern United States and southern Canada. It is the final third species we have with dimorphic inflorescences and embryos with more than one full spiral. It can be separated from the other two, Potamogeton spirillus and P. diversifolius, because it has very narrow submersed leaves without lacunae and fruits with lateral keels without sharp points. (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. diversifolius var. trichophyllus | |||||||||
Name authority | Linnaeus: Sp. Pl. 1: 127. 1753 (as pusillum) | Fernald: Memoirs of the american academy of arts and science 17: 112. (1932) | ||||||||
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