Potamogeton groenlandicus
Potamogeton epihydrus
Greenland pondweed
Nuttall's ribbon-leaf pondweed, potamot emerge, ribbon-leaf pondweed
absent.
present.
terete, without spots, 20–50 cm;
glands white, 0.1–0.7 mm diam.
flattened, without spots, 10–90 cm;
glands absent.
terminal or axillary, common, 4.2–8.4 cm × 1.4–2.5 mm, soft;
leaves ± 4-ranked;
outer leaves 2 per side, base without corrugations, apex acute to apiculate;
inner leaves unmodified.
absent.
submersed, ± spirally arranged, sessile, delicate;
stipules deliquescent to persistent, inconspicuous, convolute, free from blade, brown, not ligulate, 0.45–1.91 cm, not fibrous, not shredding at tip, apex obtuse;
blade pale to deep green, linear, not arcuate, 2.6–8.8 cm × 0.7–1.7 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or present, 0–3 rows each side of midrib;
veins 7–11.
both submersed and floating or floating absent, ± spirally arranged.
petiolate;
petioles continuous in color to apex, 2–12.5 cm;
blade adaxially light green, narrowly oblong-oblanceolate to elliptic, 2–8 cm × 4–20 mm, base acute, apex rounded or bluntly cuspidate;
veins 11–41.
sessile, lax;
stipules persistent, inconspicuous, convolute, free from blade, red-brown, not ligulate, 1–3 cm, not fibrous, not shredding at tip, apex obtuse;
blade red-brown to light green, linear, not arcuate, 5–22 cm × 1–10 mm, base not clasping, without basal lobes, margins entire, not crispate, apex not hoodlike, blunt to acute, lacunae present, broad band each side of midvein;
veins 3–13.
unbranched, emersed;
peduncles not dimorphic, terminal, erect, cylindric, 20 mm;
spikes not dimorphic, cylindric, 5 mm.
unbranched, emersed;
peduncles not dimorphic, axillary, erect, cylindric, 1.5–5(–16) cm;
spikes not dimorphic, cylindric, 0.8–4 cm.
not laterally keeled, 2.6–2.7 × 2 mm;
beak erect, 0.3 mm;
sides without basal tubercles;
embryo with 1 full coil.
sessile, greenish brown, round-obovoid, flattened, abaxially and laterally keeled, 2.5–4.5 × 2–3.6 mm, lateral keels without sharp points;
beak erect, 0.5 mm;
sides without basal tubercles;
embryo with less than 1 full spiral.
= 26.
= 26.
Potamogeton groenlandicus
Potamogeton epihydrus
Of conservation concern.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
No specimens have been seen from Maryland, but the species is to be expected there.
Two varieties, Potamogeton epihydrus var. epihydrus and var. ramosus, have been recognized. These prove not to be distinct. Both varieties often grow in the same body of water in the same population. The wider-leaved plants often occur in more alkaline waters. Two hybrids, P. epihydrus var. nuttallii × P. gramineus and P. epihydrus × P. nodosus (= P. ×subsessilis Hagström), have been described.
Potamogeton epihydrus is a common species of lakes and streams of northern United States and southern Canada. It extends southward in the eastern United States to Louisiana and Alabama. Potamogeton epihydrus is one of our more easily recognized species: it has floating leaves, linear submersed leaves, and fruits with an embryo with one full spiral or less. The only other North American pondweed with a similar set of characteristics is P. tennesseensis, which differs from P. epihydrus by the former having long tapering apices in the submersed leaves whereas the latter has blunt to acute apices.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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