Potamogeton ogdenii |
Potamogeton obtusifolius |
|
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Ogden's pondweed, potamot d'Ogden |
blunt-leaf pondweed, potamot à feuilles obtuses |
|
Rhizomes | absent. |
absent. |
Cauline stems | compressed-filiform, without spots, to 50 cm; glands green, golden brown to dark brown, 0.2–0.6 mm diam. |
slightly compressed, without spots, 35–90 cm; glands yellow-green to gold, 0.2–1 mm diam. |
Turions | terminal or lateral, uncommon, 3.7–9.9 × 2.6–6 cm, soft to hard; leaves flattened with outer and inner leaves in same plane; outer leaves 1–2 per side, base not corrugate, apex apiculate; inner leaves undifferentiated or rolled into hardened, fusiform structure. |
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 | submersed, ± spirally arranged, sessile, rigid; stipules persistent, inconspicuous, convolute, free from blade, brown or rarely white, not ligulate, 0.9–2.1 cm, slightly fibrous, partially shredding at tip, apex obtuse; blade somewhat reddish to olive-green, linear, not arcuate, 1.5–10 cm × 1.2–2.9 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, cuspidate to bristle-tipped, lacunae present or absent, in 0–3 rows each side of midvein; veins 3–9(–13). |
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. |
Inflorescences | unbranched, emersed; peduncles not dimorphic, terminal or occasionally axillary, erect or rarely recurved, slightly clavate, 1–3 cm; spikes not dimorphic, cylindric, 5–11 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, dark green, orbicular, turgid, abaxial keel obscure, lateral keels obscure or absent, 2.5–3 × 2.2–3 mm, lateral keels if present without points; beak erect, 0.5 mm; sides without basal tubercles; embryo with 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. |
Chromosome number | unknownnot available. |
|
2n | = 26. |
|
Potamogeton ogdenii |
Potamogeton obtusifolius |
|
Phenology | Flowering mid summer–fall. | Flowering and fruiting summer–fall. |
Habitat | Alkaline waters of ponds and lakes | Medium- to low-alkaline waters of lakes and slow-flowing streams |
Elevation | 100–300 m (300–1000 ft) | 50–2000 m (200–6600 ft) |
Distribution |
CT; MA; NY; VT; ON |
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 | Potamogeton ogdenii is an extremely local species, probably known from fewer than a dozen localities. The species is herein reported for the first time from Canada, being known from that country by a single collection made in 1987. 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 | Hellquist & R. L. Hilton: Systematic Botany 8: 88, figs. 1–3, plates 1–2, figs. 1–3. (1983) | Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) |
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