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

clasping-leaf pondweed, potamot de Richardson, Richardson's pondweed

Cauline stems

terete, often rust-spotted, 30–90 cm;

nodal glands absent.

terete, without spots, to 100 cm;

nodal glands absent.

Turions

absent.

absent.

Leaves

both submersed and floating, ± spirally arranged.

submersed, ± spirally arranged, sessile, lax;

stipules persistent, conspicuous, convolute, free from blade, white, not ligulate, 0.12–0.17 cm, fibrous, disintegrating to persistent fibers, even on proximal portion of stem, shredding at apex, apex obtuse;

blade olive green, ovate-lanceolate to narrowly lanceolate, not arcuate, 1.6–13 cm × 5–28 mm, base rounded, without basal lobes, clasping, margins entire to crispate, apex not hoodlike, not splitting when pressed, acute to obtuse, lacunae absent;

veins 3–35.

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.

emersed, unbranched;

peduncles not dimorphic, terminal or axillary, erect to rarely recurved, clavate, 1.5–14.8 cm;

spikes not dimorphic, cylindric, 13–37 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, greenish brown, obovoid, turgid to concave, not or rarely abaxially keeled, not laterally keeled, 2.2–4.2 × 1.7–2.9 mm;

beak erect, 0.4–0.7 mm;

sides without basal tubercles;

embryo with 1 full spiral.

Rhizome(s)

present.

present.

2n

= 52.

= 52.

Potamogeton natans

Potamogeton richardsonii

Phenology Flowering summer–fall. Flowering summer–fall.
Habitat Quiet or slow-flowing waters of ponds, lakes, and streams Alkaline waters of lakes, streams, and rivers
Elevation 0–3100 m (0–10200 ft) 0–3000 m (0–9800 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
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[BONAP county map]
from FNA
AK; CA; CO; CT; IA; ID; IL; IN; MA; ME; MI; MN; MT; ND; NE; NH; NV; NY; OH; OR; PA; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NS; NT; ON; QC; SK; YT
[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 richardsonii is quite similar to P. perfoliatus. Specific characteristics to separate the two species are the shape of the leaf blade apex, acute in P. richardsonii and obtuse in P. perfoliatus, and the condition of the stipules, disintegrating between the veins leaving fibrous strands in P. richardsonii, and the entire stipule, including the veins, disintegrating in P. perfoliatus.

Two hybrids, Potamogeton gramineus × P. richardsonii (= P. × hagstroemii A. Bennett [as hagstromii]) and P. nodosus × P. richardsonii (= P. × rectifolius A. Bennett), 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. obtusifolius, P. ogdenii, P. perfoliatus, P. praelongus, P. pulcher, P. pusillus, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. vaseyi, P. zosteriformis
Synonyms P. perfoliatus var. richardsonii, P. perfoliatus subsp. richardsonii
Name authority Linnaeus: Sp. Pl. 1: 126. (1753) (A. Bennett) Rydberg: Bulletin of the Torrey Botanical Club 32: 599. (1905)
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