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blunt-leaf pondweed, potamot à feuilles obtuses

grass-leaf pondweed, grassy pondweed, potamot à feuilles de graminées, variable pondweed, variable-leaf pondweed

Rhizomes

absent.

present.

Cauline stems

slightly compressed, without spots, 35–90 cm;

glands yellow-green to gold, 0.2–1 mm diam.

terete to flattened, without spots, to 150 cm;

nodal glands absent.

Turions

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.

absent.

Leaves

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.

both submersed and floating or submersed only, ± spirally arranged.

Floating leaves

petioles continuous in color to apex, 3–4.5 cm;

blade yellow-green to dark green, elliptic to ovate, 3.5–4 cm × 16–20 mm, base rounded, apex acuminate;

veins 11–13.

Submersed leaves

sessile or rarely petiolate, lax;

stipules persistent, inconspicuous, convolute, free from blade, pale green to brown, not ligulate, 1.3–1.6 cm, not fibrous, not shredding at tip, apex acute to obtuse;

petioles to 3 cm;

blade light green to brownish green, elliptic, not arcuate, 3.1–9.1 cm × 3–27 mm, base attenuate, without basal lobes, not clasping, margins entire, rarely crispate, apex not hoodlike, acuminate, lacunae in 1–2 rows each side of midvein;

veins 3–9.

Inflorescences

unbranched, emersed;

peduncles not dimorphic, axillary, erect, rarely recurved, cylindric, 0.8–1.9(–4.2) cm;

spike not dimorphic, cylindric, 8–13 mm.

emersed, unbranched;

peduncles not dimorphic, both axillary and terminal, erect to ascending, cylindric, 3.2–7.7 cm;

spikes not dimorphic, cylindric, 15–35 mm.

Fruits

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, greenish brown, ovoid, laterally compressed, abaxially and laterally keeled, 1.9–2.3 × 1.8–2 mm, lateral keels without points;

beak erect, 0.3–0.5 mm;

sides without basal tubercles;

embryo with less than 1 full spiral.

2n

= 26.

= 52.

Potamogeton obtusifolius

Potamogeton gramineus

Phenology Flowering and fruiting summer–fall. Flowering summer–fall.
Habitat Medium- to low-alkaline waters of lakes and slow-flowing streams Ponds, lakes, streams, and rivers
Elevation 50–2000 m (200–6600 ft) 0–3500 m (0–11500 ft)
Distribution
from FNA
AK; CT; ID; MA; ME; MI; MN; MT; NH; NJ; NY; PA; RI; VT; WA; WI; WY; AB; BC; MB; NB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
[WildflowerSearch map]
[BONAP county map]
from FNA
AK; AZ; CA; CO; CT; IA; ID; IL; IN; KS; KY; MA; MD; ME; MI; MN; MT; ND; NE; NH; NJ; NV; NY; OH; OR; PA; RI; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NL; NS; NT; NU; ON; PE; QC; SK; YT; SPM; Greenland; Eurasia
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)

Seven hybrids, Potamogeton gramineus × P. nodosus (= P. × argutulus Hagström), P. gramineus × P. richardsonii (= P. hagstroemii A. Bennett [as hagstromii]), P. alpinus × P. gramineus (= P. × nericius Hagström), P. gramineus × P. perfoliatus (= P. × nitens Weber [P. × subnitens Hagström]), P. gramineus × P. natans (= P. × sparganiifolius Laestadius ex Fries), P. gramineus × P. illinoensis [= P. × spathuliformis (J. W. Robbins) Morong)], and P. gramineus × P. praelongus (= P. × vilnensis Galinis), have been described.

Three varieties were recognized (E. C. Ogden 19435) and treated (M. L. Fernald 1950). These varieties, Potamogeton gramineus var. gramineus, deletion}P. gramineus var. myriophyllus, and P. gramineus var. maximus, were said to be separated by the shape and size of the submersed leaves. We have studied many populations of this species in the field and have observed on several occasions that a single population has leaf morphology variable enough to include all three varieties. We have, , therefore, chosen not to recognize any infraspecific categories for this species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 22. FNA vol. 22.
Parent taxa Potamogetonaceae > Potamogeton Potamogetonaceae > Potamogeton
Sibling taxa
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. gramineus, P. groenlandicus, P. hillii, P. illinoensis, P. natans, P. nodosus, P. oakesianus, P. oblongus, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
P. alpinus, P. amplifolius, P. bicupulatus, P. clystocarpus, P. confervoides, P. crispus, P. diversifolius, P. epihydrus, P. floridanus, P. foliosus, P. friesii, P. groenlandicus, P. hillii, P. illinoensis, P. natans, P. nodosus, P. oakesianus, P. oblongus, P. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
Synonyms P. gramineus var. maximus, P. gramineus var. myriophyllus
Name authority Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823) Linnaeus: Sp. Pl. 1: 127. 1753 (as gramineum)
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