Potamogeton amplifolius Tuckerman: Largeleaf pondweed, bassweed. Potamogetonaceae (pondweed family). Native perennial. This robust plant grows in water of lakes and rivers to 9 ft (2.7 m), rarely to18 ft (5.4 m). It has two types of leaves, although floating leaves are not always present. P. amplifolius is unusual for pondweeds, in that both floating and submersed leaves are wide, and the underwater leaves can be larger than those at the surface. Submersed leaves are thin and flimsy with flaccid margins; they frequently collapse or fold in half inwards, arching upwards along the prominent midrib to a crescent shape. The blades are basically oval, 3 - 8 in (7.5 - 20 cm) long, broadly pointed at the tip and tapering into the short leaf stalks. Floating leaves are flat, firm, and oval, 2 - 7 in (5 - 17.5 cm) long, and rounded, rather than tapering, at the base; 24 to 48 veins are visible on the upper surface, with several of these being ridged. The sharply pointed stipules tend to be longer than the leaf stalks of the submersed leaves and shorter than the stalks of the floating leaves; the stipules have two ridged veins down the back. The flower spike emerges from among the floating leaves; it is club-like and borne on a stout stalk.