Potamogeton praelongus |
Potamogeton gramineus |
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long-stalk pondweed, potamot à longs pédoncules, white-stalk pondweed, white-stem pondweed |
grass-leaf pondweed, grassy pondweed, potamot à feuilles de graminées, variable pondweed, variable-leaf pondweed |
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Cauline stems | terete, without spots, to 210 cm; nodal glands absent. |
terete to flattened, without spots, to 150 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 submersed only, ± spirally arranged. |
Floating leaves | petioles continuous in color to apex, 3–4.5 cm; blade yellow-green to dark green, elliptic to ovate, 3.5–4 cm × 16–20 mm, base rounded, apex acuminate; veins 11–13. |
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Submersed leaves | sessile or rarely petiolate, lax; stipules persistent, inconspicuous, convolute, free from blade, pale green to brown, not ligulate, 1.3–1.6 cm, not fibrous, not shredding at tip, apex acute to obtuse; petioles to 3 cm; blade light green to brownish green, elliptic, not arcuate, 3.1–9.1 cm × 3–27 mm, base attenuate, without basal lobes, not clasping, margins entire, rarely crispate, apex not hoodlike, acuminate, lacunae in 1–2 rows each side of midvein; veins 3–9. |
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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, both axillary and terminal, erect to ascending, cylindric, 3.2–7.7 cm; spikes not dimorphic, cylindric, 15–35 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, greenish brown, ovoid, laterally compressed, abaxially and laterally keeled, 1.9–2.3 × 1.8–2 mm, lateral keels without points; beak erect, 0.3–0.5 mm; sides without basal tubercles; embryo with less than 1 full spiral. |
Rhizome(s) | present. |
present. |
2n | = 52. |
= 52. |
Potamogeton praelongus |
Potamogeton gramineus |
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Phenology | Flowering summer–fall. | Flowering summer–fall. |
Habitat | Neutral to alkaline waters of lakes, rivers, and streams | Ponds, lakes, streams, and rivers |
Elevation | Greenland; 100–3000 m (Greenland; 300–9800 ft) | 0–3500 m (0–11500 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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AK; AZ; CA; CO; CT; IA; ID; IL; IN; KS; KY; MA; MD; ME; MI; MN; MT; ND; NE; NH; NJ; NV; NY; OH; OR; PA; RI; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NL; NS; NT; NU; ON; PE; QC; SK; YT; SPM; Greenland; Eurasia
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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.) |
Seven hybrids, Potamogeton gramineus × P. nodosus (= P. × argutulus Hagström), P. gramineus × P. richardsonii (= P. hagstroemii A. Bennett [as hagstromii]), P. alpinus × P. gramineus (= P. × nericius Hagström), P. gramineus × P. perfoliatus (= P. × nitens Weber [P. × subnitens Hagström]), P. gramineus × P. natans (= P. × sparganiifolius Laestadius ex Fries), P. gramineus × P. illinoensis [= P. × spathuliformis (J. W. Robbins) Morong)], and P. gramineus × P. praelongus (= P. × vilnensis Galinis), have been described. Three varieties were recognized (E. C. Ogden 19435) and treated (M. L. Fernald 1950). These varieties, Potamogeton gramineus var. gramineus, deletion}P. gramineus var. myriophyllus, and P. gramineus var. maximus, were said to be separated by the shape and size of the submersed leaves. We have studied many populations of this species in the field and have observed on several occasions that a single population has leaf morphology variable enough to include all three varieties. We have, , therefore, chosen not to recognize any infraspecific categories for this species. (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. gramineus var. maximus, P. gramineus var. myriophyllus | |
Name authority | Wulfen: Arch. Bot. (Leipzig) 3: 331. (1805) | Linnaeus: Sp. Pl. 1: 127. 1753 (as gramineum) |
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