Washington State Department of Ecology > Water & shorelines > Freshwater studies > Lake water quality > Aquatic Plant Guide home > Submersed Plants > Potamogeton crispus and Potamogeton zosteriformis
Aquatic Plant Identification Manual for Washington's Freshwater Plants
Submersed Plants
Potamogeton zosteriformis Fern, flat-stem or eelgrass pondweed
Both curly leaf and flat-stem pondweed grow entirely underwater except for the flower stalk which rises above the water. Curly leaf pondweed has distinctly wavy-edged, crispy olive-green to reddish-brown leaves. It usually grows early in spring and dies back in summer. The leaves of flat-stem pondweed are long and narrow with smooth edges and the sharp-edged stem is flat and about the same width as the leaves.
Leaf: Alternate, all submersed, no leaf stalks. Curly leaf: oblong, stiff, translucent leaves (4-10 cm long, 5-10 mm wide) have distinctly wavy edges with fine teeth and 3 main veins. Sheaths (stipules) up to 1 cm long are free of the leaf base and disintegrate with age. Flat-stem: smooth-edged leaves (5-20 cm long, 2-5 mm wide) have many veins. Sheaths (stipules) 2-6 cm long are free of the leaf base and become fibrous with age.
Stem: Curly leaf: branched, up to 90 cm long, somewhat flattened. Flat-stem: generally few branched, up to 2 m long, 0.7-4 mm wide, flattened, with sharp edges.
Flower: Tiny, with 4 petal-like lobes. Curly leaf: in spikes 1-3 cm long on stalks up to 7 cm long. Flat-stem: in spikes up to 3 cm long on stalks up to 10 cm long.
Fruit: Seed-like achene. Curly leaf: 4-6 mm long including 2-3 mm beak, back ridged. Flat-stem: approximately 5 mm long, sharp ridge on back, short beak (to 1 mm).
Root: Fibrous, from slender rhizomes.
Propagation: Seeds and creeping rhizomes. Curly leaf: over-winters as a hard, brown, bur-like bud with crowded, small holly-like leaves. Flat-stem: overwinters as leafy buds.
Importance of plant: Curly leaf: introduced from Eurasia, occasionally a nuisance, especially in the mid-west, but seldom considered a problem plant in Washington. Flat-stem: provides wildlife food and habitat.
Distribution: Curly leaf: nearly worldwide. Flat-stem: widespread in temperate North America; found throughout Washington.
Habitat: Curly leaf: shallow to deep still or flowing water, tolerant of disturbance. Flat-stem: ponds, lakes, 1-2.5 m deep.
May be confused with: Curly leaf: Richardson's pondweed (P. richardsonii) which has clasping leaf bases and longer, wider leaves with more pointed tips. Flat-stem: the broad, flattened, sharp-edged stems distinguish this plant.
Photographs: Potamogeton crispus, P. zosteriformis, P. zosteriformis
Line Drawings: Potamogeton crispus
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