Potamogeton tennesseensis |
Potamogeton obtusifolius |
|
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Tennessee pondweed |
blunt-leaf pondweed, potamot à feuilles obtuses |
|
Rhizomes | present. |
absent. |
Cauline stems | terete, without spots, 10–35 cm; glands absent. |
slightly compressed, without spots, 35–90 cm; glands yellow-green to gold, 0.2–1 mm diam. |
Turions | absent. |
terminal, abundant, 3.5–7.8 cm × 2.3–5.1 mm, soft; leaves ± 2-ranked; outer leaves 3–4 per side, base not corrugate, apex apiculate to obtuse; inner leaves undifferentiated. |
Leaves | both submersed and floating or floating absent, ± spirally arranged. |
submersed, ± spirally arranged, sessile, flaccid; stipules persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.6–1.8 cm, fibrous, rarely shredding at tip, apex obtuse; blade light green to somewhat reddish, linear, not arcuate, 3–8.2 cm × 1–3.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse or round-apiculate, lacunae in 1–3 rows each side of midrib; veins 3. |
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. |
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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. |
|
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, rarely recurved, cylindric, 0.8–1.9(–4.2) cm; spike not dimorphic, cylindric, 8–13 mm. |
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, olive-green to brown, obovoid, turgid, abaxially keeled or not, laterally keeled or not, 2.5–3.6 × 1.7–2.4 mm, lateral keels when present without points; beak erect, 0.8–1 mm; sides without basal tubercles; embryo with 1 full spiral. |
2n | = 26. |
|
Potamogeton tennesseensis |
Potamogeton obtusifolius |
|
Phenology | Flowering mid spring–fall. | Flowering and fruiting summer–fall. |
Habitat | Slow- to fast-moving streams and rivers | Medium- to low-alkaline waters of lakes and slow-flowing streams |
Elevation | 200–1000 m (700–3300 ft) | 50–2000 m (200–6600 ft) |
Distribution |
KY; MD; NC; OH; PA; TN; VA; WV |
AK; CT; ID; MA; ME; MI; MN; MT; NH; NJ; NY; PA; RI; VT; WA; WI; WY; AB; BC; MB; NB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
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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.) |
Potamogeton obtusifolius is a distinctive linear-leaved species with the leaf blades round at the apex, especially when fruiting inflorescences 5–7 mm wide are present. This is unusually wide for one of the linear-leaved species. Two hybrids, Potamogeton obtusifolius × P. pusillus (= P. × saxonicus Hagström) and P. friesii × obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 22. | FNA vol. 22. |
Parent taxa | ||
Sibling taxa | ||
Name authority | Fernald: Rhodora 38: 167, plate 412. (1936) | Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) |
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