Potamogeton natans L.: Floatingleaf pondweed. Potamogetonaceae (pondweed family). Native perennial. Grows in still and slow-moving water, preferring depths of about 5 ft (1.5 m). Floating and submersed leaf shapes differ; stems seldom branch. Submersed leaves are stalkless, extremely narrow, linear, and rather stiff, tapering evenly along a length of 4 - 20 in (10 - 50 cm) to a thread-like tip. Floating leaves are oval, to 4 in (10 cm) long. Leaf stalks are slender and usually longer than the blade. The base of the floating leaf blade is wider than the pointed tip; where it meets the stalk it can be slightly indented (heart-shaped) or almost straight across, making this juncture look right-angled or square-cut rather than tapered. Stipules clasp the stem; they are long and fibrous and sharply pointed at the tip. The stalk of the emergent flower spike is thicker than the leaf-bearing portion of the stem.