Potamogeton hillii |
Potamogeton epihydrus |
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Hill's pondweed |
Nuttall's ribbon-leaf pondweed, potamot emerge, ribbon-leaf pondweed |
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Rhizomes | absent. |
present. |
Cauline stems | slightly compressed, without spots, 30–60 cm; glands rare, when present, brown to green, 0.1–0.3 mm diam. |
flattened, without spots, 10–90 cm; glands absent. |
Turions | terminal, rare, 2.8–3 cm × 1.5–3 mm, soft; leaves ± 2-ranked; outer leaves 3–4 per side, base not corrugate, apex acute to apiculate; inner leaves undifferentiated. |
absent. |
Leaves | submersed, ± spirally arranged, sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, white to light brown, not ligulate, 0.7–1.6 cm, slightly fibrous, rarely shredding at tip, apex obtuse; blade pale green to olive-green, linear, not arcuate, 2–6 cm × 0.6–2.5(–4) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, apiculate to bristle-tipped or rarely blunt, lacunae in 1–2 rows each side of midrib; veins 3. |
both submersed and floating or floating absent, ± spirally arranged. |
Floating leaves | 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. |
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Submersed leaves | 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. |
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Inflorescences | unbranched, emersed; peduncles not dimorphic, axillary and/or terminal, erect to ascending, rarely recurved, slightly clavate, 6–13.5 mm; spikes not dimorphic, globose, (2–) 4–7 mm. |
unbranched, emersed; peduncles not dimorphic, axillary, erect, cylindric, 1.5–5(–16) cm; spikes not dimorphic, cylindric, 0.8–4 cm. |
Fruits | brown to light greenish brown, ovoid to orbicular, turgid, sessile, abaxially and laterally keeled (3-keeled), 2.3–4 × 2–3.2 mm, lateral keels without points; beak erect, 0.3–0.7 mm; sides without basal tubercles; embryo with 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. |
Chromosome number | unknownnot available. |
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2n | = 26. |
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Potamogeton hillii |
Potamogeton epihydrus |
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Phenology | Flowering and fruiting summer. | Flowering summer–fall. |
Habitat | Alkaline waters of marshes, ponds, lakes, and slow-moving streams | Still or flowing waters of lakes, ponds, streams, and rivers |
Elevation | 50–400 m (200–1300 ft) | 10–1900 m (0–6200 ft) |
Distribution |
CT; MA; MI; NY; OH; PA; VA; VT; WI; ON
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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 | Potamogeton hillii is an easily recognized species either in fruit or when sterile. The leaf blade has a bristle tip and five or fewer veins. Those characters combined with the usual absence of nodal glands will separate this species from all other North American linear-leaved species. Ecologically, it is consistently found in more alkaline waters than any other North American pondweed. A study of 35 localities established the mean to be 124.1 mg/l CaCO3 (C. B. Hellquist 1984). (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. porteri | P. epihydrus subsp. nuttallii, P. epihydrus var. ramosus |
Name authority | Morong: Botanical Gazette 6: 290, fig. 3. (1881) | Rafinesque: Medical Repository 5: 354. 1808, hexade hexade 2; 3; 2:409. (1811) |
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