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Washington State Department of Ecology > Water & shorelines > Freshwater studies > Lake water quality > Aquatic Plant Guide home > Submersed Plants > Najas flexilis and Najas guadalupensis

Aquatic Plant Identification Manual for Washington's Freshwater Plants

Submersed Plants

Species: Najas flexilis (Willd.) Rost & Schmidt, slender water-nymph or naiad and Najas guadalupensis (Sprengel) Magnus, common water-nymph
Family: Najadaceae

Slender water-nymph and common water-nymph are completely submerged annual plants, although they are often found as floating fragments. They have opposite leaves that are often clustered near the tips of the stems. The leaf base is much wider than the rest of the leaf blade, which helps to distinguish the water-nymphs from other underwater plants. These plants have inconspicuous flowers and fruits that are almost completely hidden by the leaf bases. Water-nymph pollination takes place underwater.
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Leaf: Glossy, green, and finely toothed leaves are oppositely arranged, but appear to be whorled near ends of the stems. The leaves are long and narrow with broad bases that clasp the stem. Slender: the leaves taper to a long point and are 1-3 cm long and 1-2 mm wide. Common: the blunt-tipped leaves are generally shorter and narrower (1-2.5 cm long and 0.5-1 mm wide) than slender water-nymph leaves.

Stem: The slender, limp and branched stem is up to 2 m long and easily broken.

Flower: Inconspicuous, tiny (2-3 mm) flowers are located in clusters at the base of the leaves. Male and female flowers occur separately on the same plant. Water-nymph pollen is transported by water currents.

Fruit: The small, oval-shaped fruit is located in the leaf bases. Each fruit contains one seed that is about 3 mm long. The fruit surface is smooth and glossy in slender water-nymph and is dull and pitted in common water-nymph. The fruits are present in late summer.

Root: Fibrous.

Propagation: Seeds, plant fragments.

Importance of plant: The entire plant is eaten by waterfowl. Water-nymphs are considered to be one of their most important food sources. They also provide shelter for small fish and insects.

Distribution: Slender: northern North America and northern Europe. Common: southern North America, Central and South America. In Washington, slender water-nymph is the more common species, but common water-nymph has been reported.

Habitat: Ponds, lakes and sluggish streams to depths of 4 m. Slender water-nymph tolerates brackish conditions.

May be confused with: The broad sheathing leaf bases and the opposite leaf arrangement help to distinguish the water-nymphs from other submersed species such as nitella (Nitella spp.), water-starwort (Callitriche spp.), muskgrass (Chara spp.), and thin-leaved pondweeds (Potamogeton spp.). Examination of seed characteristics is the only reliable method of distinguishing between slender and common water-nymph.

Photographs: Najas flexilis photograph, Najas guadalupensis photo 

Line Drawings: Najas guadalupensis

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