Potamogeton perfoliatus
Potamogeton nodosus
clasping-leaf pondweed, potamot perfolié
loddon's pondweed, long-leaf pondweed, pondweed, potamot noeuex
present.
present.
terete, without spots, to 250 cm;
nodal glands absent.
terete, without spots, to 100 cm;
nodal glands absent.
absent.
absent.
submersed, ± spirally arranged, sessile, lax;
stipules deteriorating into fibers and deciduous, inconspicuous (absent on proximal portion of stem), convolute, free from blade, light brown to green, not ligulate, 3.5–6.5 cm, not fibrous, not shredding at apex;
blade olive-green, broadly lanceolate, orbiculate, or ovate, not arcuate, 0.9–7.6(–9.7) cm × 7–40 mm, base rounded, without basal lobes, clasping, margins entire, often crispate, apex not hoodlike, not splitting when pressed, round, rarely acute;
veins 3–25.
both submersed and floating, or floating absent, ± 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.
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.
unbranched, emersed;
peduncles not dimorphic, terminal or axillary, erect to rarely recurved, cylindric, 1–7.3 cm;
spike not dimorphic, cylindric, 0.4–4.8 cm.
unbranched, emersed;
peduncles not dimorphic, terminal, erect to ascending, cylindric, 3–15 cm;
spikes not dimorphic, cylindric, 20–70 mm.
sessile, greenish brown to olive-green, obovoid, turgid or rarely concave, not abaxially or laterally keeled, 1.6–3 × 1.3–2.2 mm;
beak erect, 0.4–0.6 mm;
sides without basal tubercles;
embryo with 1 full spiral.
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.
= 52.
= 52.
Potamogeton perfoliatus
Potamogeton nodosus
Four hybrids, Potamogeton perfoliatus × P. praelongus (= P. × cognatus Ascherson & Graebner), P. perfoliatus × P. pusillus (= P. × mysticus Morong), P. gramineus × P. perfoliatus (= P. × nitens Weber [P. × subnitens Hagström]), and P. alpinus × P. perfoliatus (= P. × prussicus Hagström), have been described.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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