Potamogeton vaseyi |
Potamogeton richardsonii |
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potamot de Vasey, Vasey's pondweed |
clasping-leaf pondweed, potamot de Richardson, Richardson's pondweed |
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Cauline stems | terete, without spots, 2–5 cm; glands absent. |
terete, without spots, to 100 cm; nodal glands absent. |
Turions | 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. |
absent. |
Leaves | submersed, or both submersed and floating, ± spirally arranged. |
submersed, ± spirally arranged, sessile, lax; stipules persistent, conspicuous, convolute, free from blade, white, not ligulate, 0.12–0.17 cm, fibrous, disintegrating to persistent fibers, even on proximal portion of stem, shredding at apex, apex obtuse; blade olive green, ovate-lanceolate to narrowly lanceolate, not arcuate, 1.6–13 cm × 5–28 mm, base rounded, without basal lobes, clasping, margins entire to crispate, apex not hoodlike, not splitting when pressed, acute to obtuse, lacunae absent; veins 3–35. |
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. |
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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). |
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Inflorescences | 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. |
emersed, unbranched; peduncles not dimorphic, terminal or axillary, erect to rarely recurved, clavate, 1.5–14.8 cm; spikes not dimorphic, cylindric, 13–37 mm. |
Fruits | 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. |
sessile, greenish brown, obovoid, turgid to concave, not or rarely abaxially keeled, not laterally keeled, 2.2–4.2 × 1.7–2.9 mm; beak erect, 0.4–0.7 mm; sides without basal tubercles; embryo with 1 full spiral. |
Rhizome(s) | absent. |
present. |
2n | = 28. |
= 52. |
Potamogeton vaseyi |
Potamogeton richardsonii |
|
Phenology | Flowering and fruiting summer–fall. | Flowering summer–fall. |
Habitat | Quiet waters of lakes, ponds, and rivers | Alkaline waters of lakes, streams, and rivers |
Elevation | 50–500 m (200–1600 ft) | 0–3000 m (0–9800 ft) |
Distribution |
CT; IA; IL; IN; MA; ME; MI; MN; NH; NJ; NY; OH; PA; RI; VT; WI; NB; ON; QC
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AK; CA; CO; CT; IA; ID; IL; IN; MA; ME; MI; MN; MT; ND; NE; NH; NV; NY; OH; OR; PA; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NS; NT; ON; QC; SK; YT
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Discussion | 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.) |
Potamogeton richardsonii is quite similar to P. perfoliatus. Specific characteristics to separate the two species are the shape of the leaf blade apex, acute in P. richardsonii and obtuse in P. perfoliatus, and the condition of the stipules, disintegrating between the veins leaving fibrous strands in P. richardsonii, and the entire stipule, including the veins, disintegrating in P. perfoliatus. Two hybrids, Potamogeton gramineus × P. richardsonii (= P. × hagstroemii A. Bennett [as hagstromii]) and P. nodosus × P. richardsonii (= P. × rectifolius A. Bennett), 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. perfoliatus var. richardsonii, P. perfoliatus subsp. richardsonii | |
Name authority | J. W. Robbins: in A. Gray, Manual of Botany of the Northern United States (ed. 5) 485. (1867) | (A. Bennett) Rydberg: Bulletin of the Torrey Botanical Club 32: 599. (1905) |
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