Potamogeton nodosus Poir.: American pondweed, longleaf pondweed. Potamogetonaceae (pondweed family). Native perennial. Submersed plant, growing rooted in substrate from slender white rhizomes marked with red. The stem, growing to 6 ft (1.8 m), carries two forms of leaves, submersed and floating, both alternate. Submersed leaves have slender stalks to 6 in (15 cm); blades are narrow and linear, pointed at the tip and tapering to the stalk, 8 in (20 cm) long; they are thin and flimsy. Floating leaves, lying flat on the surface, are oval, rather leathery and shiny, to 4.3 in (11 cm) long, the blades taper to leaf stalks that are up to 8 in (20 cm) long. From 7 to 15 veins can be counted on the upper side, and the underside has a prominent midvein. Stipules at the base of the leaves are relatively long, to 4 in (10 cm), and pointed; those underwater are more frayed and fibrous. Flower stalks, thicker than the stem, arise from nodes of floating leaves to emerge from the water; they carry club-like spikes of densely packed, inconspicuous flowers.