Potamogeton perfoliatus
Potamogeton natans
clasping-leaf pondweed, potamot perfolié
broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat
present.
present.
terete, without spots, to 250 cm;
nodal glands absent.
terete, often rust-spotted, 30–90 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, ± 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.
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.
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, 4.5–9.5 cm;
spikes not dimorphic, cylindric, 25–50 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, 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.
= 52.
= 52.
Potamogeton perfoliatus
Potamogeton natans
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.)
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.)
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