Potamogeton oblongus auct. non Viv.: Aitch.
Perennial, rhizomatous, aquatic. Stem branched, leafy, terete, simple. Leaves heterophyllous, submerged leaves petiolate, lanceolate or broadly lanceolate-oblong, veins 9 or more, thin translucent, 6-10.5 cm long; floating leaves broadly ovate, elliptic, coriaceous, of firm texture, 4-16 cm long, 2-5 cm broad, entire. Stipules free, keeled, lanceolate 2-15 cm long, 8-10 mm broad. Spikes cylindric, 4.5-11 cm long, 1.5-2.5 mm broad; peduncle 7-11 cm long. Flowers in whorls, sessile, small. Perianth segments small, obtuse, entire, c. 1.5 mm long. Stigma short. Fruitlets 3-4 mm long, 2-3 mm broad, obliquely obovoid, spongy, ventral margin convex, shortly beaked.
Fl. Per.: April-August.
Type: Canary Islands, Broussonet..
Distribution: Warmer regions of Europe, N. and Cent. America, Africa and Asia.
Sometimes confused with Potamogeton natans L., but submerged leaves not reduced to narrowly linear phyllodes, and petioles without discoloured joints at the tips. Common from hills to the plains of our area.