Potamogeton obtusifolius |
Potamogeton vaseyi |
|
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blunt-leaf pondweed, potamot à feuilles obtuses |
potamot de Vasey, Vasey's pondweed |
|
Rhizomes | absent. |
absent. |
Cauline stems | slightly compressed, without spots, 35–90 cm; glands yellow-green to gold, 0.2–1 mm diam. |
terete, without spots, 2–5 cm; glands absent. |
Turions | 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. |
common, axillary, 0.5–2 cm × 0.5–1.2 mm, soft; leaves ± 2-ranked; outer leaves 2–3 per side, base not corrugate, apex acute; inner leaves undifferentiated or rolled into tight, hardened structure. |
Leaves | 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. |
submersed, or both submersed and floating, ± spirally arranged. |
Floating leaves | petioles continuous in color to apex, 5–25 mm; blade adaxially greenish brown, elliptic, spatulate, or obovate, 0.6–1.5 cm × 3–8 mm, base acute, apex obtuse; veins 5–9. |
|
Submersed leaves | sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, green to brown, not ligulate, 0.4–1.2 cm, not fibrous, not shredding at tip, apex attenuate; blade light green, linear-filiform, not arcuate, 2–8 cm × 0.1–1 mm, bases slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to almost bristle-tipped, lacunae present, rarely absent, 0–2 rows each side of midvein; veins 1(–3). |
|
Inflorescences | unbranched, emersed; peduncles not dimorphic, axillary, erect, rarely recurved, cylindric, 0.8–1.9(–4.2) cm; spike not dimorphic, cylindric, 8–13 mm. |
unbranched, emersed; peduncles not dimorphic, terminal, ascending in flower, recurved in fruit, cylindric, 5–30 mm; spikes not dimorphic, cylindric or moniliform, 6–8 mm. |
Fruits | 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. |
sessile, green to brown, obliquely round-obovoid, compressed, abaxially keeled, not laterally keeled, 1.5–2.5 × 1.2–1.6 mm; beak erect, 0.3–0.5 mm; sides without basal tubercles; embryo with 1 full spiral. |
2n | = 26. |
= 28. |
Potamogeton obtusifolius |
Potamogeton vaseyi |
|
Phenology | Flowering and fruiting summer–fall. | Flowering and fruiting summer–fall. |
Habitat | Medium- to low-alkaline waters of lakes and slow-flowing streams | Quiet waters of lakes, ponds, and rivers |
Elevation | 50–2000 m (200–6600 ft) | 50–500 m (200–1600 ft) |
Distribution |
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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CT; IA; IL; IN; MA; ME; MI; MN; NH; NJ; NY; OH; PA; RI; VT; WI; NB; ON; QC
|
Discussion | 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.) |
All of the original material of Potamogeton lateralis Morong, including the collection designated as the lectotype, has been studied (C. B. Hellquist et al. 1988). Every specimen, was a mixed collection of P. pusillus and P. vaseyi. Based on the results of the study, P. lateralis is taxonomically nomenclaturally invalid and should be rejected. Potamogeton vaseyi is an uncommon species that has submersed leaves very similar to P. pusillus subsp. gemmiparus. Floating leaves apparently are present only when the species is fertile, and the species often grows intermixed with that subspecies. Collections are consequently often a mixture of the two taxa. Also, sterile collections of either taxon can easily be mistaken for the other. (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 | ||
Name authority | Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) | J. W. Robbins: in A. Gray, Manual of Botany of the Northern United States (ed. 5) 485. (1867) |
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