South American Waterweed (Egeria densa)

Gallery:

South American waterweed

South American waterweed floating on the surface

submerged South American waterweed

South American waterweed flower

Common names:

South American waterweed, Brazilian elodea, common waterweed, Brazilian waterweed, dense waterweed, egeria, leafy elodea

Scientific Name:

Egeria densa

Description:

South American waterweed is a perennial aquatic plant in the Hydrocharitaceae (frogbit) family. It was introduced as a dumped aquarium plant and can be found all over western Oregon, especially along the coast. This leafy plant grows underwater in freshwater systems, and is sometimes free floating. The flowers bloom above the surface and are white with three petals. The leaves occur in whorls of 4 to 8 (mostly 4), are bright green, up to 1 inch long, and finely serrated. As only male plants have been found in the US, it doesn’t create seed; the primary reproduction method is through root and stem fragments, which easily break off and root elsewhere.

Life cycle:

Perennial

Height of mature plants

Often 1-2 feet, but it can grow up to 10 feet

Flower color:

white

Bloom time:

July and August

Look-a-likes:

South Americam waterweed looks similar to American waterweed (E. canadensis) and hydrilla (Hydrilla verticillata). However, American waterweed is much smaller and less robust, generally has only 3 leaves per whorl, and leaves are usually less than 1 cm long. Hydrilla has 5 leaves per whorl, tiny spines along the leaf margins, and also produces tubers.

Habitat:

South American waterweed is an aquatic, submerged, freshwater plant, and thus it grows in lakes, ponds, quiet streams and ditches. It is usually rooted to the bottom in depths up to 8 feet, but is also often found in floating masses.

Impacts:

South American waterweed can grow quite thick in waterways, creating obstructions to boating, fishing and swimming. The thick mats of this weed can also impede water flow, clog water pumps, shade out other aquatic plants and degrade the water quality. As an aquatic plant that also spreads by root and stem fragments, it can be quite difficult to control.