Potamogeton amplifolius
Potamogeton floridanus
big-leaf pondweed, broad-leaf pondweed, large-leaf pondweed, potamot à grandes feuilles
Florida pondweed
present.
present.
terete, often rusty spotted, 6–110 cm;
nodal glands absent.
terete, without spots, ca. 50 cm.
absent.
unknown.
both submersed and floating or floating absent, ± spirally arranged.
submersed and floating, ± spirally arranged.
petioles continuous in color to apex, 2.3–22.6 cm;
blade adaxially light green, lanceolate to round elliptic, 4.3–9.2 cm × 25–38 mcm, base rounded to cordate, apex acute to rounded;
veins 27–49.
petioles continuous in color to apex, 4–6.5 cm;
blade adaxially dark brown, elliptic, 4.5–6.6 cm × 7–12 mm;
base acute, apex acute;
veins 7–11.
petiolate, lax;
stipules persistent, conspicuous, convolute, free from blade, light brown, not ligulate, 1.5–11.7 cm, not fibrous, not shredding at tip, apex acute;
petioles terete, 0.9–11.5 cm;
blade light to dark green, ovate to oblanceolate, distinctly arcuate, 5–12.5 cm × 15–58 mm, base rounded to acute, without basal lobes, not clasping, margins entire, crispate, apex not hoodlike, acute to round-apiculate, lacunae absent;
veins 19–49.
sessile, lax;
stipules persistent, inconspicuous, convolute, free from blade, whitish, not ligulate, 2.5–4 cm, delicately fibrous, eventually shredding, apex acute;
blade dark green to olive-green, narrowly linear, not arcuate, 15–20 cm × 0.7 mm, base attenuate, not clasping, not lobed, margins entire, not crispate, apex not hoodlike, acute, lacunae absent;
veins 1.
unbranched, emersed;
peduncles not dimorphic, terminal or axillary, erect, cylindric, 4.5–22.3 cm;
spikes not dimorphic, cylindric, 34–65 mm.
unknown.
sessile, reddish brown, obovoid, turgid, abaxially keeled, laterally ridged, 5–6.7 × 4.5–5.2 mm, lateral ridges without points;
beak erect, 0.5–0.8 mm;
sides without basal tubercles;
embryo with full spiral.
unknown.
= 52.
Potamogeton amplifolius
Potamogeton floridanus
No specimens have been seen from Kentucky or Texas, but the species is to be expected there.
Potamogeton amplifolius is common throughout much of North America. Its submersed leaves are larger than those of most other species of Potamogeton, are arcuate, and have more veins than do any other species.
One hybrid, Potamogeton amplifolius × P. illinoensis (= P. × scoliophyllus Hagström), has been described.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Potamogeton floridanus is an extremely localized species of the panhandle of Florida. No one has treated the species recently (E. C. Ogden 1943; R. R. Haynes 1978). Four populations of the taxon were reported from Santa Rosa County, Florida (G. S. Wilhelm and R. H. Mohlenbrock 1986). Those populations clearly match the protologue and the original collections. One population has recently been found fertile (J. R. Burckhalter, pers. comm.), but we have not examined the specimens. Because the taxon persists and has a vegetative morphology unlike any other pondweed, we believe it must be recognized. Until a better understanding of the taxon is developed, we prefer to recognize it at the specific level.
Of conservation concern.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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