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flat-stalk pondweed, Fries' pondweed, potamot de Fries

potamot de Vasey, Vasey's pondweed

Rhizomes

absent.

absent.

Cauline stems

compressed, without spots, 10–135 cm;

glands green, greenish brown, or gold, to 0.7 mm diam.

terete, without spots, 2–5 cm;

glands absent.

Turions

terminal or lateral, common, 1.5–5 cm × 1.5–4 mm, soft;

leaves ± 4-ranked;

outer leaves 2–3 per side, base corrugate, apex apiculate to acute;

inner leaves reduced, arranged into fan-shaped structure and oriented at 90° angles to outer leaves.

common, axillary, 0.5–2 cm × 0.5–1.2 mm, soft;

leaves ± 2-ranked;

outer leaves 2–3 per side, base not corrugate, apex acute;

inner leaves undifferentiated or rolled into tight, hardened structure.

Leaves

submersed, ± spirally arranged, delicate to rigid, sessile;

stipules not persistent, inconspicuous, convolute, free from blade, white, not ligulate, 0.55–2.1 cm, fibrous, coarse, shredding at tip, apex obtuse;

blade light green, rarely olive-green to.somewhat reddish, linear, not arcuate, 2.3–6.5 cm × 1.2–3.2 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to apiculate, lacunae absent or 1 narrow row each side of midrib;

veins 5–7(–9).

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

Floating leaves

petioles continuous in color to apex, 5–25 mm;

blade adaxially greenish brown, elliptic, spatulate, or obovate, 0.6–1.5 cm × 3–8 mm, base acute, apex obtuse;

veins 5–9.

Submersed leaves

sessile, delicate;

stipules persistent, inconspicuous, convolute, free from blade, green to brown, not ligulate, 0.4–1.2 cm, not fibrous, not shredding at tip, apex attenuate;

blade light green, linear-filiform, not arcuate, 2–8 cm × 0.1–1 mm, bases slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to almost bristle-tipped, lacunae present, rarely absent, 0–2 rows each side of midvein;

veins 1(–3).

Inflorescences

unbranched, emersed;

peduncles not dimorphic, terminal or axillary, erect or rarely recurved, slightly clavate, 1.2–4.1(–7) cm;

spike not dimorphic, cylindric, 7–16 mm.

unbranched, emersed;

peduncles not dimorphic, terminal, ascending in flower, recurved in fruit, cylindric, 5–30 mm;

spikes not dimorphic, cylindric or moniliform, 6–8 mm.

Fruits

sessile, olive-green to brown, obovoid, turgid, not abaxially or laterally keeled, 1.8–2.5 × 1.2–2 mm;

beak erect, 0.3–0.7 mm;

sides without basal tubercles;

embryo with 1 full spiral.

sessile, green to brown, obliquely round-obovoid, compressed, abaxially keeled, not laterally keeled, 1.5–2.5 × 1.2–1.6 mm;

beak erect, 0.3–0.5 mm;

sides without basal tubercles;

embryo with 1 full spiral.

2n

= 26.

= 28.

Potamogeton friesii

Potamogeton vaseyi

Phenology Flowering and fruiting summer–fall. Flowering and fruiting summer–fall.
Habitat Calcareous to brackish waters of lakes and slow-flowing streams Quiet waters of lakes, ponds, and rivers
Elevation 0–3100 m (0–10200 ft) 50–500 m (200–1600 ft)
Distribution
from FNA
AK; CO; CT; IA; ID; IL; IN; MA; ME; MI; MN; MT; ND; NE; NH; NY; OH; PA; RI; SD; UT; VT; WA; WI; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; Eurasia
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[BONAP county map]
from FNA
CT; IA; IL; IN; MA; ME; MI; MN; NH; NJ; NY; OH; PA; RI; VT; WI; NB; ON; QC
[WildflowerSearch map]
[BONAP county map]
Discussion

Potamogeton friesii is a fairly common linear-leaved species, especially of calcareous waters of lakes and streams of the upper Midwest. Whenever turions are present, the species is easily identified, as it is the only one with the outer leaves of the turions having corrugate bases and the inner leaves turned at right angles to the outer leaves.

Two hybrids, Potamogeton friesii × P. pusillus (= P. × pusilliformis Fischer [P. × intermedius Fischer]) and P. friesii × P. obtusifolius (= P. × semifructus A. Bennett ex Ascherson & Graebner), have been described.

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

All of the original material of Potamogeton lateralis Morong, including the collection designated as the lectotype, has been studied (C. B. Hellquist et al. 1988). Every specimen, was a mixed collection of P. pusillus and P. vaseyi. Based on the results of the study, P. lateralis is taxonomically nomenclaturally invalid and should be rejected.

Potamogeton vaseyi is an uncommon species that has submersed leaves very similar to P. pusillus subsp. gemmiparus. Floating leaves apparently are present only when the species is fertile, and the species often grows intermixed with that subspecies. Collections are consequently often a mixture of the two taxa. Also, sterile collections of either taxon can easily be mistaken for the other.

(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. 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. 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. richardsonii, P. robbinsii, P. spirillus, P. strictifolius, P. subsibiricus, P. tennesseensis, P. zosteriformis
Name authority Ruprecht: Hist. Stirp. Fl. Petrop. 43. (1845) J. W. Robbins: in A. Gray, Manual of Botany of the Northern United States (ed. 5) 485. (1867)
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