Potamogeton hillii
Potamogeton floridanus
Hill's pondweed
Florida pondweed
absent.
present.
slightly compressed, without spots, 30–60 cm;
glands rare, when present, brown to green, 0.1–0.3 mm diam.
terete, without spots, ca. 50 cm.
terminal, rare, 2.8–3 cm × 1.5–3 mm, soft;
leaves ± 2-ranked;
outer leaves 3–4 per side, base not corrugate, apex acute to apiculate;
inner leaves undifferentiated.
unknown.
submersed, ± spirally arranged, sessile, delicate;
stipules persistent, inconspicuous, convolute, free from blade, white to light brown, not ligulate, 0.7–1.6 cm, slightly fibrous, rarely shredding at tip, apex obtuse;
blade pale green to olive-green, linear, not arcuate, 2–6 cm × 0.6–2.5(–4) mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, apiculate to bristle-tipped or rarely blunt, lacunae in 1–2 rows each side of midrib;
veins 3.
submersed and floating, ± spirally arranged.
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, 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, axillary and/or terminal, erect to ascending, rarely recurved, slightly clavate, 6–13.5 mm;
spikes not dimorphic, globose, (2–) 4–7 mm.
unknown.
brown to light greenish brown, ovoid to orbicular, turgid, sessile, abaxially and laterally keeled (3-keeled), 2.3–4 × 2–3.2 mm, lateral keels without points;
beak erect, 0.3–0.7 mm;
sides without basal tubercles;
embryo with 1 full spiral.
unknown.
unknownnot available.
Potamogeton hillii
Potamogeton floridanus
Potamogeton hillii is an easily recognized species either in fruit or when sterile. The leaf blade has a bristle tip and five or fewer veins. Those characters combined with the usual absence of nodal glands will separate this species from all other North American linear-leaved species. Ecologically, it is consistently found in more alkaline waters than any other North American pondweed. A study of 35 localities established the mean to be 124.1 mg/l CaCO3 (C. B. Hellquist 1984).
(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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