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broad-leaf pondweed, floating pondweed, floating-leaf pondweed, potamot flottat

blunt-leaf pondweed, potamot à feuilles obtuses

Rhizomes

present.

absent.

Cauline stems

terete, often rust-spotted, 30–90 cm;

nodal glands absent.

slightly compressed, without spots, 35–90 cm;

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

Turions

absent.

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.

Leaves

both submersed and floating, ± spirally arranged.

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.

Floating leaves

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.

Submersed leaves

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.

Inflorescences

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, axillary, erect, rarely recurved, cylindric, 0.8–1.9(–4.2) cm;

spike not dimorphic, cylindric, 8–13 mm.

Fruits

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, 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.

2n

= 52.

= 26.

Potamogeton natans

Potamogeton obtusifolius

Phenology Flowering summer–fall. Flowering and fruiting summer–fall.
Habitat Quiet or slow-flowing waters of ponds, lakes, and streams Medium- to low-alkaline waters of lakes and slow-flowing streams
Elevation 0–3100 m (0–10200 ft) 50–2000 m (200–6600 ft)
Distribution
from FNA
AK; AZ; CA; CO; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NH; NJ; NM; NV; NY; OH; OR; PA; RI; SD; UT; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
[WildflowerSearch map]
[BONAP county map]
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]
Discussion

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 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.)

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. 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
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
Name authority Linnaeus: Sp. Pl. 1: 126. (1753) Mertens & W. D. J. Koch: in J. C. Röhling et al., Deutschl. Fl., ed. 3 1: 855. (1823)
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