Potamogeton praelongus |
Potamogeton illinoensis |
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long-stalk pondweed, potamot à longs pédoncules, white-stalk pondweed, white-stem pondweed |
Illinois pondweed, pondweed, potamot de i'Illinois, shining pondweed |
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Cauline stems | terete, without spots, to 210 cm; nodal glands absent. |
terete, without spots, 28–120 cm; nodal glands absent. |
Turions | absent. |
absent. |
Leaves | submersed, ± spirally arranged, sessile, lax; stipules persistent, conspicuous, convolute, free from blade, white to green, not ligulate, 3–8.1 cm, fibrous, shredding at apex; blade pale green, rarely olive green, linear-lanceolate, not arcuate, 0.8–2.8 cm × 11–46 mm, base clasping, without basal lobes, margins entire, rarely crispate, apex hoodlike, splitting when pressed, obtuse, lacunae absent; veins 11–33. |
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 | emersed, unbranched; peduncles not dimorphic, terminal or axillary, erect to spreading, cylindric, 9.5–53 cm; spikes not dimorphic, cylindric, 34–75 mm. |
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, obovoid, turgid, abaxially keeled, occasionally laterally keeled, 4–5.7 × 3.2–4 mm, lateral keels when present without points; beak erect, 0.6–1 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. |
Rhizome(s) | present. |
present. |
2n | = 52. |
= 104. |
Potamogeton praelongus |
Potamogeton illinoensis |
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Phenology | Flowering summer–fall. | Flowering and fruiting summer–fall. |
Habitat | Neutral to alkaline waters of lakes, rivers, and streams | Alkaline waters of streams, rivers, lakes, ponds, and sloughs |
Elevation | Greenland; 100–3000 m (Greenland; 300–9800 ft) | 0–2700 m (0–8900 ft) |
Distribution |
AK; CA; CO; CT; IA; ID; IN; MA; ME; MI; MN; MT; NE; NH; NJ; NY; OR; PA; SD; UT; VT; WI; WY; AB; BC; MB; NB; NF; NS; NT; NU; ON; PE; QC; SK; YT; Mexico; Greenland; Eurasia
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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 | Potamogeton praelongus is one of the easiest pondweeds to identify with its submersed leaves only clasping the more or less zigzagged stem. The persistent, hugelarge, white stipules provide another clue to this species. Four hybrids, Potamogeton perfoliatus × P. praelongus (= P. × cognatus Ascherson & Graebner), P. alpinus × P. praelongus (= P. × griffithii A. Bennett), P. crispus × P. praelongus (= P. × undulatus Wolfgang ex Schultes & Schultes f.), and P. gramineus × P. praelongus (= P. × vilnensis Galinus), 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 | Potamogetonaceae > Potamogeton | Potamogetonaceae > Potamogeton |
Sibling taxa | ||
Name authority | Wulfen: Arch. Bot. (Leipzig) 3: 331. (1805) | Morong: Botanical Gazette 5: 50. (1880) |
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