Stem: Up to 3 m in length. Leaves occur along the entire length of the stem. 

Flower: Fragrant white flowers have a yellow center with three, 7-9 mm long petals. Flowers float on the water surface and are attached at the base of leaf whorls by long slender stalks (to 6 cm). Two to three flower stalks may arise from the same whorl. Male and female flowers are produced on separate plants, but only male plants are found in the United States. The plant flowers from late spring to early fall.

Fruit: Fruits and seeds have not been observed outside of its native range.

Root: Fibrous. Can produce white advantitious roots along the stem.

Propagation: Because only male plants are found here, propagation is from stem fragments and by collapsed stems that sprout roots and form the base of new plants. Dormant shoots develop in the fall and overwinter in the sediment.

Importance of plant: Crowds out native species. Eaten by wildlife, although not preferred forage.

Distribution: South American native. Introduced to North America via the aquarium trade. Occurs in some Northwest lakes and rivers and is considered to be a nuisance.

Habitat: Lakes, ponds, sloughs, streams. 

May be confused with: Hydrilla (Hydrilla verticillata), another non-native invasive species. Hydrilla has tubers, the leaves are more spiny in appearance and usually occur in whorls of 5. Common waterweed (Elodea canadensis) has smaller leaves in whorls of 3.

Photographs: Egeria densa closeup 

Line Drawings: Egeria densa