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long-stalk pondweed, potamot à longs pédoncules, white-stalk pondweed, white-stem pondweed

Oakes' pondweed, potamot d'Oakes

Cauline stems

terete, without spots, to 210 cm;

nodal glands absent.

terete, with red spots, 7–75 cm;

nodal glands absent.

Turions

absent.

absent.

Leaves

submersed, ± spirally arranged, sessile, lax;

stipules persistent, conspicuous, convolute, free from blade, white to green, not ligulate, 3–8.1 cm, fibrous, shredding at apex;

blade pale green, rarely olive green, linear-lanceolate, not arcuate, 0.8–2.8 cm × 11–46 mm, base clasping, without basal lobes, margins entire, rarely crispate, apex hoodlike, splitting when pressed, obtuse, lacunae absent;

veins 11–33.

both submersed and floating, ± spirally arranged.

Floating leaves

petioles continuous in color to apex, 3.2–7.5 cm;

blade adaxially light to dark green, lanceolate to elliptic or ovate, (1.5–)2–4(–5.5) cm × 10–20(–30) mm, base rounded or tapering, apex acute;

veins (7–)9–19(–23).

Submersed leaves

sessile, lax;

stipules persistent, conspicuous, convolute, free from blade, whitish, not ligulate, 1–3 cm, delicately fibrous, not shredding at tip, apex obtuse;

blade pale green, linear to phyllodial, not arcuate, 5–16 cm × (0.25–)0.3–1 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex acute, not hoodlike, lacunae absent, setaceous;

veins 3.

Inflorescences

emersed, unbranched;

peduncles not dimorphic, terminal or axillary, erect to spreading, cylindric, 9.5–53 cm;

spikes not dimorphic, cylindric, 34–75 mm.

unbranched, emersed;

peduncles not dimorphic, terminal, ascending to spreading, cylindric, 2.5–8 cm;

spikes not dimorphic, cylindric, 10–35 mm.

Fruits

sessile, greenish brown, obovoid, turgid, abaxially keeled, occasionally laterally keeled, 4–5.7 × 3.2–4 mm, lateral keels when present without points;

beak erect, 0.6–1 mm;

sides without basal tubercles;

embryo with 1 full spiral.

sessile, greenish brown, obovoid, turgid, abaxially keeled, laterally keeled, 2.5–3.5(–3.7) × (1.6–)2–2.4 mm, lateral keels without points;

beak erect, 0.4–0.8 mm;

sides without basal tubercles;

embryo with 1 full spiral.

Chromosome number

apparently unknown.

Rhizome(s)

present.

present.

2n

= 52.

Potamogeton praelongus

Potamogeton oakesianus

Phenology Flowering summer–fall. Flowering summer–fall.
Habitat Neutral to alkaline waters of lakes, rivers, and streams Quiet acidic waters of bogs, ponds, and lakes
Elevation Greenland; 100–3000 m (Greenland; 300–9800 ft) 50–1500 m (200–4900 ft)
Distribution
from FNA
AK; CA; CO; CT; IA; ID; IN; MA; ME; MI; MN; MT; NE; NH; NJ; NY; OR; PA; SD; UT; VT; WI; WY; AB; BC; MB; NB; NF; NS; NT; NU; ON; PE; QC; SK; YT; Mexico; Greenland; Eurasia
[WildflowerSearch map]
[BONAP county map]
from FNA
CT; MA; ME; MI; MN; MT; NH; NJ; NY; PA; RI; VA; VT; WI; WV; BC; NB; NL; NS; ON; QC; SPM
[WildflowerSearch map]
[BONAP county map]
Discussion

Potamogeton praelongus is one of the easiest pondweeds to identify with its submersed leaves only clasping the more or less zigzagged stem. The persistent, hugelarge, white stipules provide another clue to this species.

Four hybrids, Potamogeton perfoliatus × P. praelongus (= P. × cognatus Ascherson & Graebner), P. alpinus × P. praelongus (= P. × griffithii A. Bennett), P. crispus × P. praelongus (= P. × undulatus Wolfgang ex Schultes & Schultes f.), and P. gramineus × P. praelongus (= P. × vilnensis Galinus), have been described.

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

Potamogeton oakesianus, along with Potamogeton floridanus and P. natans, has floating leaves and phyllodial submersed leaves. The petioles of this species and of P. floridanus lack a short area of light-colored tissue immediately proximal to the blade.

(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. obtusifolius, P. ogdenii, P. perfoliatus, 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. 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
Name authority Wulfen: Arch. Bot. (Leipzig) 3: 331. (1805) J. W. Robbins: in A. Gray, Manual of Botany of the Northern United States (ed. 5) 485. (1867)
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