Potamogeton natans
Potamogeton friesii
broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat
flat-stalk pondweed, Fries' pondweed, potamot de Fries
present.
absent.
terete, often rust-spotted, 30–90 cm;
nodal glands absent.
compressed, without spots, 10–135 cm;
glands green, greenish brown, or gold, to 0.7 mm diam.
absent.
terminal or lateral, common, 1.5–5 cm × 1.5–4 mm, soft;
leaves ± 4-ranked;
outer leaves 2–3 per side, base corrugate, apex apiculate to acute;
inner leaves reduced, arranged into fan-shaped structure and oriented at 90° angles to outer leaves.
both submersed and floating, ± spirally arranged.
submersed, ± spirally arranged, delicate to rigid, sessile;
stipules not persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.55–2.1 cm, fibrous, coarse, shredding at tip, apex obtuse;
blade light green, rarely olive-green to.somewhat reddish, linear, not arcuate, 2.3–6.5 cm × 1.2–3.2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or 1 narrow row each side of midrib;
veins 5–7(–9).
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, erect to ascending, cylindric, 4.5–9.5 cm;
spikes not dimorphic, cylindric, 25–50 mm.
unbranched, emersed;
peduncles not dimorphic, terminal or axillary, erect or rarely recurved, slightly clavate, 1.2–4.1(–7) cm;
spike not dimorphic, cylindric, 7–16 mm.
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.
sessile, olive-green to brown, obovoid, turgid, not abaxially or laterally keeled, 1.8–2.5 × 1.2–2 mm;
beak erect, 0.3–0.7 mm;
sides without basal tubercles;
embryo with 1 full spiral.
= 52.
= 26.
Potamogeton natans
Potamogeton friesii
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 friesii is a fairly common linear-leaved species, especially of calcareous waters of lakes and streams of the upper Midwest. Whenever turions are present, the species is easily identified, as it is the only one with the outer leaves of the turions having corrugate bases and the inner leaves turned at right angles to the outer leaves.
Two hybrids, Potamogeton friesii × P. pusillus (= P. × pusilliformis Fischer [P. × intermedius Fischer]) and P. friesii × P. obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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