Potamogeton L.

Inflorescence usually more than 2-flowered. Carpels 4. Mature fruit ± sessile Potamogeton
Leaves distinctly petiolate; the upper ones with a floating lamina; a few of the lower ones submerged and of a different shape
Floating leaves narrow-oblong to elliptic or lanceolate, 2–3 cm long, 5 mm wide; submerged leaves linear, 3–10 cm long. Spikes narrow, 2–3 cm long, on slender peduncles. Coast. Uncommon. Fl. spring–summer P. javanicus javanicusP. javanicus
Floating leaves cordate to elliptic-ovate, 5–10 cm long. Fruits c. 3 mm long, with 3 dorsal ridges. Spikes dense, 25–50 mm long, on rather stout peduncles. Floating leaves with 15–25 veins; submerged leaves narrow-lanceolate. Widespread. Fl. spring–autumn P. tricarinatus tricarinatusP. tricarinatus