Potamogeton bicupulatus |
Potamogeton obtusifolius |
|
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snail-seed pondweed |
blunt-leaf pondweed, potamot à feuilles obtuses |
|
Rhizomes | present. |
absent. |
Cauline stems | compressed, without spots, 10–25 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, 5–35 mm; blade adaxially light green, lanceolate-elliptic to broadly elliptic, 0.6–2.3(–2.8) cm × 1–11 mm, base tapering or rounded, apex acute to long tapering; veins 3–7. |
|
Submersed leaves | sessile, lax; stipules persistent to deliquescent, inconspicuous, convolute, adnate to blade for less than ½ stipule length, light green, ligulate, 0.2–1.2 cm, not fibrous, not shredding at tip, apex obtuse; blade light green to rarely brown, linear-setaceous, not arcuate, 1.5–11 cm × 0.1–0.4(–0.6) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, tapering, lacunae absent; veins 1. |
|
Inflorescences | unbranched; peduncles dimorphic, submersed axillary, somewhat recurved, clavate, 1–10 mm, emersed axillary or terminal, erect to slightly recurved, slightly clavate, 3.5–22 mm; spikes dimorphic, submersed, globular to ellipsoid, 1.5–7 mm, emersed ellipsoid to cylindric, 3–14 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, somewhat orbicular, compressed, abaxially keeled, laterally keeled, 1.1–2.1 × 1.1–2 mm, lateral keel without points; beak absent; sides without basal tubercles; embryo with more 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 bicupulatus |
Potamogeton obtusifolius |
|
Phenology | Flowering early summer–fall. | Flowering and fruiting summer–fall. |
Habitat | Acidic waters of ponds, lakes, and streams | Medium- to low-alkaline waters of lakes and slow-flowing streams |
Elevation | 0–300 m (0–1000 ft) | 50–2000 m (200–6600 ft) |
Distribution |
CT; DE; IN; MA; ME; MI; NH; NY; PA; RI; TN; VA; VT; WI; 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
|
Discussion | Potamogeton bicupulatus is an uncommon species of the acid lakes and streams of northeastern United States and southern Canada. It is the final third species we have with dimorphic inflorescences and embryos with more than one full spiral. It can be separated from the other two, Potamogeton spirillus and P. diversifolius, because it has very narrow submersed leaves without lacunae and fruits with lateral keels without sharp points. (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 | Potamogetonaceae > Potamogeton | Potamogetonaceae > Potamogeton |
Sibling taxa | ||
Synonyms | P. diversifolius var. trichophyllus | |
Name authority | Fernald: Memoirs of the american academy of arts and science 17: 112. (1932) | Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) |
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