Potamogeton alpinus |
Potamogeton natans |
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alpine pondweed, northern pondweed, potamot alpin, reddish pondweed |
broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat |
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Cauline stems | terete, without spots, to 200 cm; nodal glands absent. |
terete, often rust-spotted, 30–90 cm; nodal glands absent. |
Turions | absent. |
absent. |
Leaves | submersed and floating or floating absent, ± spirally arranged. |
both submersed and floating, ± spirally arranged. |
Floating leaves | petioles continuous in color to apex, 0.1–1.2 cm; blade reddish green, elliptic or oblanceolate to obovate or oblong-linear, 4–7(–10) cm × 10–25(–40) mm, base gradually tapering into petiole, apex obtuse or acute; veins (7–)9–13(–15). |
petioles lighter green immediately proximal to apex, 5.5–29 cm; blade adaxially light green, elliptic to ovate, 3.5–11 cm × 15–60 mm, base cordate, apex acute to rounded; veins 17–37. |
Submersed leaves | sessile, lax; stipules persistent, inconspicuous, convolute, free from blade, light brown to reddish, not ligulate, (1.2–)1.5–2.5(–4) cm, not fibrous, not shredding at tip, apex blunt; blade reddish green, oblong-linear to linear-lanceolate, not arcuate, 4.5–18(–25) cm × 5–20 mm, base rounded, without basal lobes, slightly clasping, margins entire, not crispate, apex not hoodlike, obtuse or acute, lacunae in 0–6 rows each side of midvein; veins 7–9. |
sessile, rigid; stipules persistent, conspicuous, convolute, free from blade, whitish, not ligulate, 4.5–1 cm, fibrous, not shredding at tip, apex obtuse; blade light to dark green, phyllodial, not arcuate, 9–20 cm × 0.7–2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse, lacunae absent; veins 3–5, obscure. |
Inflorescences | unbranched, emersed; peduncles not dimorphic, terminal or axillary, erect, cylindric, 3–10(–16) cm; spikes not dimorphic, cylindric, 10–35 mm. |
unbranched, emersed; peduncles not dimorphic, terminal, erect to ascending, cylindric, 4.5–9.5 cm; spikes not dimorphic, cylindric, 25–50 mm. |
Fruits | pedicellate, tawny olive-green, obovoid, plump, turgid, abaxially keeled, laterally keeled or not, (2.5–)3–3.5 × (1.7–)2–2.4 mm, lateral keels when present without points; beak abaxially curved, 0.5–0.9 mm; sides without basal tubercles; embryo with 1 full spiral. |
sessile, green to greenish brown, obovoid, turgid, not abaxially or laterally keeled, 3.5–5 × 2–3 mm; beak erect to apically recurved, 0.4–0.8 mm; sides without basal tubercles; embryo with 1 full spiral. |
Rhizome(s) | present. |
present. |
2n | = 52. |
= 52. |
Potamogeton alpinus |
Potamogeton natans |
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Phenology | Flowering early summer–fall. | Flowering summer–fall. |
Habitat | Ponds, lakes, and slow-moving streams | Quiet or slow-flowing waters of ponds, lakes, and streams |
Elevation | 400–2500 m (1300–8200 ft) | 0–3100 m (0–10200 ft) |
Distribution |
AK; CA; CO; ID; MA; ME; MI; MN; MT; NH; NJ; NV; NY; OR; PA; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NL; NS; NT; NU; ON; PE; QC; SK; YT; Greenland; Europe; Asia Eurasia
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AK; AZ; CA; CO; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NH; NJ; NM; NV; NY; OH; OR; PA; RI; SD; UT; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
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Discussion | Plants of Potamogeton alpinus often are red whenever taken from the water, a feature that makes this species quite distinctive. Two varieties, Potamogeton alpinus var. tenuifolius and var. subellipticus, have been recognized in North America, based mainly on submersed leaf shape. Plants bearing both leaf types have been observed in the same population; hence the varieties are not recognized. Four hybrids, Potamogeton alpinus × P. nodosus (= P. ×subobtusus Hagström), P. alpinus × P. gramineus (= P. xnericius Hagström), P. alpinus × P. praelongus (= P. ×griffithii A. Bennett), and P. alpinus × P. perfoliatus (= P. ×prussicus Hagström), have been described. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Potamogeton natans is the common floating-leaved pondweed of the north temperate ure areas. It is essentially circumboreal and can easily be identified by floating leaves that are almost always cordate at the base of the blade, the petiole with a short band of light tissue at its apex, and the submersed phyllodial leaves. Also, the apex of the petiole usually is bent so that the blade appears oriented in the opposite direction from which the petiole appears to be oriented. One hybrid, Potamogeton natans × P. nodosus (= P. × schreberi Fischer [P. × perplexus A. Bennett]), has been described. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 22. | FNA vol. 22. |
Parent taxa | Potamogetonaceae > Potamogeton | Potamogetonaceae > Potamogeton |
Sibling taxa | ||
Synonyms | P. alpinus subsp. tenuifolius, P. alpinus var. subellipticus, P. alpinus var. tenuifolius, P. tenuifolius, P. tenuifolius var. subellipticus | |
Name authority | Balbis: Misc. Bot. 13. (1804) | Linnaeus: Sp. Pl. 1: 126. (1753) |
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