Potamogeton nodosus
Potamogeton floridanus
loddon's pondweed, long-leaf pondweed, pondweed, potamot noeuex
Florida pondweed
present.
present.
terete, without spots, to 100 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 3.5–26 cm;
blade adaxially light green, lenticular to elliptic, 3–11 cm × 15–45 mm, base cuneate to rounded, apex acute to rounded;
veins 9–21.
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 to deliquescent, conspicuous, convolute, free from blade, light brown, not ligulate, 3–9 cm, not fibrous, not shredding at tip, apex round to acute;
petioles 2–13 cm;
blade light to dark green, linear-lanceolate to lance-elliptic, not arcuate, 9–20 cm × 10–35 mm, base acute, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, without sharp awl-like tip, lacunae in 2–5 rows each side of midrib;
veins 7–15.
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, erect to ascending, cylindric, 3–15 cm;
spikes not dimorphic, cylindric, 20–70 mm.
unknown.
sessile, red to reddish brown, obovoid, abaxially keeled, laterally ridged, 2.7–4.3 × 2.5–3 mm, keel well developed, lateral ridges with blunt to sharp tips;
beak erect;
sides without basal tubercles;
embryo with 1 full spiral.
unknown.
= 52.
Potamogeton nodosus
Potamogeton floridanus
Six hybrids, Potamogeton gramineus × P. nodosus (= P. × argutulus Hagström), P. illinoensis × P. nodosus (= P. × faxonii Morong), P. nodosus × P. richardsonii (= P. × rectifolius A. Bennett), P. natans × P. nodosus (= P. × schreberi Fischer [P. × perplexus A. Bennett]), P. alpinus × P. nodosus (= P. × subotusus Hagström), and P. epihydrus × P. nodosus (= P. × subsessilis Hagström), have been described.
Potamogeton nodosus is a common floating-leaved species throughout much of the United States and southern Canada. When both submersed and floating leaves are present, it is very easily recognized by the petioles of the submersed leaves being longer than 5 cm.
(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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