Potamogeton oblongus

Rhizome present. Cauline stems terete, without spots, 5–30 cm; nodal glands absent. Turions absent. Leaves both submersed and floating or only submersed, ± spirally arranged. Submersed leaves petiolate, lax; stipules persistent, conspicuous, convolute, free from blade, greenish, not ligulate, to 3 cm, not fibrous, not shredding at tip, apex acute; petioles 1–3(–8) cm; blade dark green, lanceolate to occasionally ovate, occasionally arcuate, 3–13 cm × 4–15(–44) mm, base acute, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute, lacunae in 2–4 rows each side of midvein; veins 7–11. Floating leaves: petioles continuous in color to apex, 1–17 cm; blade adaxially reddish brown, ovate, 3–8(–10) cm × 10–46 mm, base rounded or slightly cordate, apex obtuse, acute, or somewhat apiculate; veins (11–)15–19(–21). Inflorescences unbranched, emersed; peduncles not dimorphic, erect to slightly recurved, cylindric, 4–12 cm; spikes not dimorphic, cylindric, 20–40 mm. Fruits sessile, dark reddish brown, obovoid to orbicularoid, compressed, not abaxially or laterally keeled, (1.6–)2–2.5 × (1.2–)1.5–2.1 mm; beak minute or obsolete, recurved; sides without basal tubercles; embryo with 1 full spiral. 2n = 26.

Phenology: Flowering July–August.
Habitat: Acid to neutral waters of ponds, lakes, and occasionally streams
Elevation: 10–100 m

Introduced; St. Pierre and Miquelon, Nfld. and Labr. (Nfld.), N.S., Europe, n Africa, Atlantic Islands (Azores).

Discussion

Selected References

None.

Lower Taxa