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FNA | Family List | FNA Vol. 22 | Potamogetonaceae | Potamogeton

21. Potamogeton oakesianus J. W. Robbins in A. Gray, Manual of Botany of the Northern United States (ed. 5). 485. 1867.

Oakes pondweed, potamot d’Oakes

Rhizomes present. Cauline stems terete, with red spots, 7--75 cm; nodal glands absent. Turions absent. Leaves both submersed and floating, ± spirally arranged. 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. 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). Inflorescences 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, 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.

Flowering summer--fall. Quiet acidic waters of bogs, ponds, and lakes; 50--1500 m; St. Pierre and Miquelon; B.C., N.B., Nfld. and Labr., N.S., Ont., Que.; Conn., Maine, Mass., Mich., Minn., Mont., N.H., N.J., N.Y., Pa., R.I., Vt., Va., W.Va., Wis.

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.


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