Ogden's pondweed, potamot d’Ogden

Rhizomes absent. Cauline stems compressed-filiform, without spots, to 50 cm; glands green, golden brown to dark brown, 0.2--0.6 mm diam. Turions terminal or lateral, uncommon, 3.7--9.9 ´ 2.6--6 cm, soft to hard; leaves flattened with outer and inner leaves in same plane; outer leaves 1--2 per side, base not corrugate, apex apiculate; inner leaves undifferentiated or rolled into hardened, fusiform structure. Leaves submersed, ± spirally arranged, sessile, rigid; stipules persistent, inconspicuous, convolute, free from blade, brown or rarely white, not ligulate, 0.9--2.1 cm, slightly fibrous, partially shredding at tip, apex obtuse; blade somewhat reddish to olive-green, linear, not arcuate, 1.5--10 cm ´ 1.2--2.9 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, cuspidate to bristle-tipped, lacunae present or absent, in 0--3 rows each side of midvein; veins 3--9(--13). Inflorescences unbranched, emersed; peduncles not dimorphic, terminal or occasionally axillary, erect or rarely recurved, slightly clavate, 1--3 cm; spikes not dimorphic, cylindric, 5--11 mm. Fruits sessile, dark green, orbicular, turgid, abaxial keel obscure, lateral keels obscure or absent, 2.5--3 ´ 2.2--3 mm, lateral keels if present without points; beak erect, 0.5 mm; sides without basal tubercles; embryo with 1 full spiral. Chromosome number unknownnot available.

Flowering mid summer--fall. Alkaline waters of ponds and lakes; of conservation concern; 100--300 m; Ont.; Conn., Mass., N.Y., Vt.

Potamogeton ogdenii is an extremely local species, probably known from fewer than a dozen localities. The species is herein reported for the first time from Canada, being known from that country by a single collection made in 1987.