Potamogeton natans
Potamogeton floridanus
broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat
Florida pondweed
present.
present.
terete, often rust-spotted, 30–90 cm;
nodal glands absent.
terete, without spots, ca. 50 cm.
absent.
unknown.
both submersed and floating, ± spirally arranged.
submersed and floating, ± spirally arranged.
petioles lighter green immediately proximal to apex, 5.5–29 cm;
blade adaxially light green, elliptic to ovate, 3.5–11 cm × 15–60 mm, base cordate, apex acute to rounded;
veins 17–37.
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.
sessile, rigid;
stipules persistent, conspicuous, convolute, free from blade, whitish, not ligulate, 4.5–1 cm, fibrous, not shredding at tip, apex obtuse;
blade light to dark green, phyllodial, not arcuate, 9–20 cm × 0.7–2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse, lacunae absent;
veins 3–5, obscure.
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, 4.5–9.5 cm;
spikes not dimorphic, cylindric, 25–50 mm.
unknown.
sessile, green to greenish brown, obovoid, turgid, not abaxially or laterally keeled, 3.5–5 × 2–3 mm;
beak erect to apically recurved, 0.4–0.8 mm;
sides without basal tubercles;
embryo with 1 full spiral.
unknown.
= 52.
Potamogeton natans
Potamogeton floridanus
Potamogeton natans is the common floating-leaved pondweed of the north temperate ure areas. It is essentially circumboreal and can easily be identified by floating leaves that are almost always cordate at the base of the blade, the petiole with a short band of light tissue at its apex, and the submersed phyllodial leaves. Also, the apex of the petiole usually is bent so that the blade appears oriented in the opposite direction from which the petiole appears to be oriented.
One hybrid, Potamogeton natans × P. nodosus (= P. × schreberi Fischer [P. × perplexus A. Bennett]), 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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