Photographer: Leslie J. Mehrhoff, University of Connecticut Source: Bugwood.org Copyright: CC 3.0 US
Brazilian waterweed, sometimes referred to as Brazilian Elodea when it was thought to be in the Elodea genus, is a submerged aquatic plant. The lancelet leaves are in whorls of 4-6, and are ½ wide and ¾- 2½ inches long. The 3-petaled, white flowers are 3/8 to ¾ in diameter and appear above the water surface for pollination. It is a rooted plant but it can survive and grow as fragments.
In smaller populations this plant can provide habitats for many invertebrates, and food for ducks and fish, but when this plant grows to large populations severe ecological changes occur. This aggressive plant is able to successfully invade new aquatic environments and outcompete native vegetation. It forms dense mats which limits sunlight below the surface, reducing oxygen, and killing fish and invertebrates below. As with other invasive aquatic plants, Egeria densa is able to impede water flow which increases flooding risks, and hinder recreational activities. These plant is spread by flooding, waterfowl, and human recreational activities.
This plant is dioecious in its native land. However, in the western United States, populations are comprised of flowering male plants. The flowers rise about 1½ inches above the water’s surface, and no seeds are produced. Since there are no seeds, plants reproduce by free-floating pieces that can root and start new plants.
It was first introduced to the United States in 1893, through the aquarium trade. Most likely this plant was able to reach natural areas from people emptying out aquarium tanks into nearby lakes and streams. It is now present in 37 states.
eastern South America
U.S. Habitat: Slow-current or still waters such as, lakes, canals, ponds, reservoirs, ditches and some creeks and rivers.
U.S. Present: AL, AR, AZ, CA, CT, DE, FL, GA, HI, ID, IL, IN, KS, KY, MA, MD, MN, MO, MS, NC, NE, NH, NJ, NM, NY, OK, OR, RI, SC, TN, TX, UT, VA, VT, and WA.
For a county distribution map provided the EDDMapS click here.
It can resemble native Elodea species, as it was once classified under the Elodea genus. The invasive aquatic plant Hydrilla (Hydrilla verticillata) also strongly resembles Brazilian waterweed. Flowers of Brazilian waterweed are larger than Hydrilla, and its leaves are larger than Elodea and in whorls of 4 to 6 and not 3 as with Elodea.
Unfortunately this plant is still commonly sold in the aquarium trade under the name Egeria or Anacharis. Do not purchase this plant for your aquarium, and NEVER dump out aquariums with aquatic plants or live fish into nearby water sources. Throw them away in trash bags, and seal them shut before placing them in trash bins.
Prevention is the key to maintain populations, and preventing it spread into other states. ALWAYS REMEMBER TO CLEAN YOUR BOAT, HULLS, AND GEAR THOUROUGHLY. Any plant fragments found should also disposed of in a trash bin, and not thrown back in the water.
Researchers, state, and federal agencies have been trying many forms of integrated control plans. These plans include mechanical and chemical control, but in most cases the plants have survived. Studies are ongoing trying to find a biological control for this invasive aquatic, but nothing has proven successful yet.
USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing.
Cook, C.D. and K. Urmi-König. 1984. A revision of the genus Egeria (Hydrocharitaceae). Aquatic Botany 19(1-2):73-96.
Weed Control in Natural Areas in the Western United States: Brazilian egeria (2013; PDF | 209 KB)
University of California. Weed Research and Information Center.
Yarrow, M., V.H. Marin, M. Finlayson, A. Tironi, L.E. Delgado, and F. Fischer. 2009. The ecology of Egeria densa Planchon (Liliopsida: Alismatales): A wetland ecosystem engineer? Revista Chilena de Historia Natural 82:299-313