Potamogeton perfoliatus |
Potamogeton illinoensis |
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clasping-leaf pondweed, potamot perfolié |
Illinois pondweed, pondweed, potamot de i'Illinois, shining pondweed |
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Rhizomes | present. |
present. |
Cauline stems | terete, without spots, to 250 cm; nodal glands absent. |
terete, without spots, 28–120 cm; nodal glands absent. |
Turions | absent. |
absent. |
Leaves | submersed, ± spirally arranged, sessile, lax; stipules deteriorating into fibers and deciduous, inconspicuous (absent on proximal portion of stem), convolute, free from blade, light brown to green, not ligulate, 3.5–6.5 cm, not fibrous, not shredding at apex; blade olive-green, broadly lanceolate, orbiculate, or ovate, not arcuate, 0.9–7.6(–9.7) cm × 7–40 mm, base rounded, without basal lobes, clasping, margins entire, often crispate, apex not hoodlike, not splitting when pressed, round, rarely acute; veins 3–25. |
both submersed and floating or the floating absent, ± spirally arranged. |
Floating leaves | petioles continuous in color to apex, 2–9 cm; blade adaxially light green, elliptic to oblong-elliptic, 4–19 cm × 20–65 mm, base cuneate, apex round-mucronate; veins 13–29. |
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Submersed leaves | sessile or petiolate, lax; stipules persistent, conspicuous, convolute, free from blade, light brown to red-brown, not ligulate, 1–8 cm, not fibrous, not shredding at tip, apex acuminate; petioles if present 0.5–4 cm; blade red-brown to light green, elliptic to lanceolate or rarely linear, often arcuate, 5–20 cm × 2–45 mm, base acute, margins entire, often crispate, apex not hoodlike, acute-mucronate, lacunae in 2–5 rows each side midrib; veins 7–19. |
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Inflorescences | unbranched, emersed; peduncles not dimorphic, terminal or axillary, erect to rarely recurved, cylindric, 1–7.3 cm; spike not dimorphic, cylindric, 0.4–4.8 cm. |
emersed, unbranched; peduncles not dimorphic, terminal or axillary, erect to ascending, cylindric, 4–30 cm; spikes not dimorphic, cylindric, 25–70 mm. |
Fruits | sessile, greenish brown to olive-green, obovoid, turgid or rarely concave, not abaxially or laterally keeled, 1.6–3 × 1.3–2.2 mm; beak erect, 0.4–0.6 mm; sides without basal tubercles; embryo with 1 full spiral. |
sessile, grayish green to olive green, obovoid to ovoid, laterally compressed, abaxially keeled, laterally ridged, 2.5–3.6 × 2.1–3 mm, abaxial keel well developed, lateral ridges without points; beak erect to slightly recurved, 0.5–0.8 mm; sides without basal tubercles; embryo with 1 full spiral. |
2n | = 52. |
= 104. |
Potamogeton perfoliatus |
Potamogeton illinoensis |
|
Phenology | Flowering summer–fall. | Flowering and fruiting summer–fall. |
Habitat | Waters, often brackish, of lakes, streams, rivers, and bays | Alkaline waters of streams, rivers, lakes, ponds, and sloughs |
Elevation | 0–100 m (0–300 ft) | 0–2700 m (0–8900 ft) |
Distribution |
AL; CT; DC; DE; FL; LA; MA; MD; ME; NC; NH; NJ; NY; OH; PA; RI; VA; VT; NB; NL; NS; ON; PE; QC; SPM; Africa; Greenland; Eurasia; Central America (Guatemala); Australia
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AL; AR; CA; CO; CT; FL; GA; IA; IL; IN; KS; KY; MA; MD; MI; MN; MO; MT; NC; NE; NH; NJ; NY; OH; OK; OR; PA; SC; SD; TX; UT; VA; VT; WA; WI; WV; WY; BC; MB; NB; NT; ON; QC; Mexico; Central America; South America; West Indies
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Discussion | Four hybrids, Potamogeton perfoliatus × P. praelongus (= P. × cognatus Ascherson & Graebner), P. perfoliatus × P. pusillus (= P. × mysticus Morong), P. gramineus × P. perfoliatus (= P. × nitens Weber [P. × subnitens Hagström]), and P. alpinus × P. perfoliatus (= P. × prussicus Hagström), have been described. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Potamogeton illinoensis and P. gramineus are often difficult to separate. Certainly, in the extreme of each they are easily separated, but they continually grade into each other. Features to look for are the acute-mucronate apex of the submersed leaves of P. illinoensis and the acuminate apex for P. gramineus. Also, the number of veins seems to work as well. Three hybrids, Potamogeton illinoensis × P. nodosus (= P. × faxonii Morong), P. amplifolius × P. illinoensis (= P. × scoliophyllus Hagström), and P. gramineus × P. illinoensis [= P. × spathuliformis (J. W. Robbins) Morong], 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 | Linnaeus: Sp. Pl. 1: 126. 1753 (as perfoliatum) | Morong: Botanical Gazette 5: 50. (1880) |
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