Potamogeton obtusifolius
Potamogeton confervoides
blunt-leaf pondweed, potamot à feuilles obtuses
alga pondweed, alga-like pondweed, potamot confervoide, Tuckerman's pondweed
absent.
obvious.
slightly compressed, without spots, 35–90 cm;
glands yellow-green to gold, 0.2–1 mm diam.
terete, without spots, 10–80 cm.
terminal, abundant, 3.5–7.8 cm × 2.3–5.1 mm, soft;
leaves ± 2-ranked;
outer leaves 3–4 per side, base not corrugate, apex apiculate to obtuse;
inner leaves undifferentiated.
present, in axils of old leaves and from disintegrating branches, fusiform, 0.7–2 cm, leaves spreading to ascending.
submersed, ± spirally arranged, sessile, flaccid;
stipules persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.6–1.8 cm, fibrous, rarely shredding at tip, apex obtuse;
blade light green to somewhat reddish, linear, not arcuate, 3–8.2 cm × 1–3.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, obtuse or round-apiculate, lacunae in 1–3 rows each side of midrib;
veins 3.
submersed, ± spirally arranged, flaccid, sessile;
stipules deliquescent, inconspicuous, convolute, free from blade, pale green, not ligulate, 0.5–1.2 cm, not fibrous, not shredding at tip, apex obtuse;
blade pale green, linear, not arcuate, 1.8–6.5 cm × 0.1–0.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, extremely attenuate, bristly, lacunae present, each side of midvein to margins;
veins 1.
unbranched, emersed;
peduncles not dimorphic, axillary, erect, rarely recurved, cylindric, 0.8–1.9(–4.2) cm;
spike not dimorphic, cylindric, 8–13 mm.
unbranched, emersed;
peduncles not dimorphic, terminal, ascending, somewhat clavate, (3–)5–25 cm;
spikes not dimorphic, capitate, 5–12 mm.
sessile, olive-green to brown, obovoid, turgid, abaxially keeled or not, laterally keeled or not, 2.5–3.6 × 1.7–2.4 mm, lateral keels when present without points;
beak erect, 0.8–1 mm;
sides without basal tubercles;
embryo with 1 full spiral.
sessile, light green, round-obovoid or nearly orbicular, compressed, abaxially and laterally keeled, 2–3 × 1.7–2.8 mm, lateral keels without sharp point;
beak erect, 0.5 mm;
sides without basal tubercles;
embryo with less than 1 full spiral.
apparently unknown not available.
= 26.
Potamogeton obtusifolius
Potamogeton confervoides
Potamogeton obtusifolius is a distinctive linear-leaved species with the leaf blades round at the apex, especially when fruiting inflorescences 5–7 mm wide are present. This is unusually wide for one of the linear-leaved species.
Two hybrids, Potamogeton obtusifolius × P. pusillus (= P. × saxonicus Hagström) and P. friesii × obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Potamogeton confervoides is most uncommon and found only in fairly acidic waters. It is easily recognized by its linear, bristly leaves and the unusually long peduncle that seems out of place on a plant with such fine leaves. The leaves are so fine that they almost appear as greenish colored hair in the water. When the plant is removed from the water, the leaves are extremely flaccid leaves and essentially collapse onto each other.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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