Potamogeton tennesseensis |
Potamogeton epihydrus |
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Tennessee pondweed |
Nuttall's ribbon-leaf pondweed, potamot emerge, ribbon-leaf pondweed |
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Rhizomes | present. |
present. |
Cauline stems | terete, without spots, 10–35 cm; glands absent. |
flattened, without spots, 10–90 cm; glands absent. |
Turions | absent. |
absent. |
Leaves | both submersed and floating or floating absent, ± spirally arranged. |
both submersed and floating or floating absent, ± spirally arranged. |
Floating leaves | petiolate; petioles continuous in color to apex, 2.5–6 cm; blade greenish brown adaxially, lance-oblong, 2–4(–5.5) cm × 5–13 mm, base acute, apex acute; veins 9–23. |
petiolate; petioles continuous in color to apex, 2–12.5 cm; blade adaxially light green, narrowly oblong-oblanceolate to elliptic, 2–8 cm × 4–20 mm, base acute, apex rounded or bluntly cuspidate; veins 11–41. |
Submersed leaves | sessile, lax; stipules persistent, inconspicuous, convolute, adnate to blade for ¼ or less stipule length, light brown to dark green, ligulate, 0.5–1.5 cm, not fibrous, not shredding at tip, apex acute; blade red-brown to dark green, linear-filiform, not arcuate, 2.5–10.5 cm × 0.2–1(–2) mm, base slightly tapering, not clasping, without basal lobes, margins entire, not crispate, apex not hoodlike, long tapering, lacunae abundant, broad, filling area between margin and midvein; veins 1–3. |
sessile, lax; stipules persistent, inconspicuous, convolute, free from blade, red-brown, not ligulate, 1–3 cm, not fibrous, not shredding at tip, apex obtuse; blade red-brown to light green, linear, not arcuate, 5–22 cm × 1–10 mm, base not clasping, without basal lobes, margins entire, not crispate, apex not hoodlike, blunt to acute, lacunae present, broad band each side of midvein; veins 3–13. |
Inflorescences | unbranched, emersed; peduncle not dimorphic, axillary, ascending, cylindric, 3–8 cm; spikes not dimorphic, cylindric, 10–22 mm. |
unbranched, emersed; peduncles not dimorphic, axillary, erect, cylindric, 1.5–5(–16) cm; spikes not dimorphic, cylindric, 0.8–4 cm. |
Fruits | sessile, greenish brown, quadrate-orbicular, slightly compressed, abaxially keeled, laterally ridged, 2.5–3 × 2–2.5 mm; lateral ridges without points; beak present, erect, 0.5 mm; sides without basal tubercles; embryo with less than 1 full spiral. |
sessile, greenish brown, round-obovoid, flattened, abaxially and laterally keeled, 2.5–4.5 × 2–3.6 mm, lateral keels without sharp points; beak erect, 0.5 mm; sides without basal tubercles; embryo with less than 1 full spiral. |
2n | = 26. |
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Potamogeton tennesseensis |
Potamogeton epihydrus |
|
Phenology | Flowering mid spring–fall. | Flowering summer–fall. |
Habitat | Slow- to fast-moving streams and rivers | Still or flowing waters of lakes, ponds, streams, and rivers |
Elevation | 200–1000 m (700–3300 ft) | 10–1900 m (0–6200 ft) |
Distribution |
KY; MD; NC; OH; PA; TN; VA; WV |
AK; AL; CA; CO; CT; DE; FL; GA; IA; ID; IN; LA; MA; MD; ME; MI; MN; MS; MT; NC; NH; NJ; NY; OH; OR; PA; RI; SC; SD; TN; UT; VA; VT; WA; WI; WV; WY; BC; MB; NB; NL; NS; ON; PE; QC; SK; SPM; Europe
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Discussion | No specimens have been seen from Maryland although the species is to be expected there. Of conservation concern. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
No specimens have been seen from Maryland, but the species is to be expected there. Two varieties, Potamogeton epihydrus var. epihydrus and var. ramosus, have been recognized. These prove not to be distinct. Both varieties often grow in the same body of water in the same population. The wider-leaved plants often occur in more alkaline waters. Two hybrids, P. epihydrus var. nuttallii × P. gramineus and P. epihydrus × P. nodosus (= P. ×subsessilis Hagström), have been described. Potamogeton epihydrus is a common species of lakes and streams of northern United States and southern Canada. It extends southward in the eastern United States to Louisiana and Alabama. Potamogeton epihydrus is one of our more easily recognized species: it has floating leaves, linear submersed leaves, and fruits with an embryo with one full spiral or less. The only other North American pondweed with a similar set of characteristics is P. tennesseensis, which differs from P. epihydrus by the former having long tapering apices in the submersed leaves whereas the latter has blunt to acute apices. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 22. | FNA vol. 22. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | P. epihydrus subsp. nuttallii, P. epihydrus var. ramosus | |
Name authority | Fernald: Rhodora 38: 167, plate 412. (1936) | Rafinesque: Medical Repository 5: 354. 1808, hexade hexade 2; 3; 2:409. (1811) |
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