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Potamogeton illinoensis:
Illinois pondweed
Potamogeton illinoensis Morong: Illinois pondweed. Potamogetonaceae (pondweed family).
Native perennial. Plants found in water to 15 ft (4.5 m) deep. Slender rhizomes form a network in the substrate; they can have red mottling. Stem is stout and branching, to 6 ft (1.8 m). Submersed and floating leaves differ, although floating leaves are often absent. Submersed leaves are linear lance-shaped, tapering at both ends, and up to 8 in (20 cm) long; a leaf stalk may be present, to 2 in (5 cm) long, or absent. These underwater leaves are thin-textured and flimsy, their edges often wavy or rippling. There is a prominent midrib on the underside; leaves may arch, but not into as pronounced a crescent-shape as in P. amplifolius. Floating leaves have a longer leaf stalk; blades are broad, leathery, oval, to 5.5 in (14 cm) long, 2.75 in (7 cm) wide, tapering or rounded at either end, and often forming a hard point at the tip. Stipules are as long as the leaf stalks of the floating leaves, firm and persistent, with two ribs or keels along the outer side. The stalk of the club-like flower spike is thicker than the stem.
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