Potamogeton zosterformis Fern.: Flatstem pondweed, fern pondweed, eelgrass pondweed. Potamogetonaceae (pondweed family). Native perennial. Found in still or slow-moving water, 3.3 - 8.2 ft (1 - 2.5 m) deep, rooting from slender rhizomes. This pondweed has only submersed leaves of a single shape, and few branches. The underwater stem is flattened, or strap-like, with slight projections or wings that produce a running edge. Leaves arise alternately along the flat stem; they are narrow, linear, without a leaf stalk, smooth-edged, coming to a sharp, tough little point at the tip and narrowing slightly at the base, usually 4 - 8 in (10 - 20 cm) long, and somewhat wider than the stem. They have a smooth margin, and 3 main parallel veins. Stipules, 0.4 - 2.4 in (1 - 6 cm) long, are attached to the nodes only at the base; they fray with age. The stem of the club-like flower spike emerges from water and is usually curved.