Varieties of Elodea plants found throughout the world
Eldoea (Elodea canadensis) - Native to United States
Perennial aquatic plant growing completely submerged in water. Soft green curled leaves grow in groups of three. Stems are frequently branched and a single plant can be up to 3 metres in length. Pieces of the plant continue to grow while floating unattached in the water.
Problem: Reduces water flow. May disrupt river traffic.
(from North Texas Water Garden Society (http://www.ntwgs.org/articles/illegalAquatics.html)
Hydrilla, commonly known as Florida Elodea, is also called star vine or oxygen plant. It has also been called Serpicula verticillata, H. alternifolia and H. dentata The exact number of species in the genus is unclear.
Hydrilla has long stems with branch freely. Leaves are 0.4 to 0.8 inches long and 0.08 to 0.2 inches wide and have toothed edges (up to 10-15 teeth) and a toothed midrib on the lower leaf surface. Leaves on the middle and upper stem segments occur in whorls of 2-8 with 4-5 whorls being the most likely configuration. Leaf midveins are often red, however, green midveins are not uncommon. Hydrilla usually feels rough to the touch. Flowers are small, about 0.16 inch across, with 3 white petals, bisexual and appear in sets of 3's.
Hydrilla often floats at the surface where it forms dense mats. It can survive under a variety of conditions including shade, brackish water, and in either still or flowing water. Hydrilla grows so rapidly that it crowds or shades more desirable aquatic plants.
Hydrilla is easily confused with Elodea spp. (which is not restricted) and Egeria densa (which is restricted). Elodea spp (elodea, American elodea, waterweed, or Dutch moss) does not have teeth on the lower leaf midrib and leaves usually appear in whorls of 3. Egeria densa (egeria, Brazilian elodea, anacharis or Elodea densa) has longer leaves (0.6 to 1.2 inches), more teeth on the leaf edge (25-35), and no spines on the lower midvein. Both Elodea spp. and Egeria densa are soft to the touch and have separate flower sexes.
Brazilian elodea (Egeria densa) - Is Not Native to United States
Class B Noxious Weed
As its name indicates, Brazilian elodea is from South America and was originally introduced to North America for aquarium use. Up until 1996 it was commonly sold in Washington pet stores and plant nurseries.
Method of Spread
Brazilian elodea reproduces by the spread of plant fragments. Branches sprout from "double nodes" located at intervals along the stems. The plant is probably spread most often when aquariums are dumped in our lakes or when boaters carry it from an infested lake into an uninfested waterbody.
Brazilian elodea grows very well in Washington lakes once introduced and soon forms dense mats that choke out our native aquatic plants. These mats are unsightly, interfere with swimming, boating and fishing, and provide poor habitat for fish.
Methods of control
Brazilian elodea is difficult to control because it has few natural predators. Some aquatic herbicides are effective in controlling its growth. Grass carp have shown promise as a control technique, but are not an option in lakes with anadromous fish runs (salmon). Harvesting allows small plant fragments to spread to new areas, limiting its success as a control method.
General Information about Brazilian Elodea
Brazilian elodea (Egeria densa) is an attractive, robust plant well-suited to aquarium life. Up until 1996 it was commonly sold in Washington pet stores under the name "anacharis." It was also sold in plant nurseries as an "oxygen" plant. Because of its invasive properties that allow it take over in waterbodies where it is introduced, it is no longer being sold in Washington.
Unfortunately Brazilian elodea grows very well in Washington lakes when thoughtless people dispose of aquarium contents in our lakes or when boaters carry it from an infested lake into an uninfested waterbody. Because Brazilian elodea is from South America and was originally imported disease and insect free for the aquarium trade, it has few natural predators to keep its growth in check. When introduced to a lake, it soon forms dense mats that choke out our native aquatic plants. These mats are unsightly, interfere with swimming, boating, fishing, and water skiing and provide poor habitat for fish. Brazilian elodea has been introduced into many lakes in western Washington (follow this link to see which lakes it is found in). Because the lakes are not close together, we believe that most infestations are the result of people dumping aquariums into the lake.
Once introduced, Brazilian elodea reproduces by the spread of plant fragments. Because all the Brazilian elodea plants in the United States are male, no seeds are produced. Branches sprout from "double nodes" located at about eight inch intervals along the stems. If a Brazilian elodea fragment does not have a "double node", it can not grow into a new plant.
In lakes where Brazilian elodea is established, it may outcompete Eurasian watermilfoil (milfoil). Harvesting tends to spread the plant around and some aquatic herbicides do not effectively control its growth. Stocking sterile (triploid) grass carp does show promise as a control technique because Brazilian elodea is highly palatable and older grass carp will eat it in preference to other plants. However, stocking grass carp is not an option in Washington lakes with anadromous fish runs (salmon or steelhead) or in lakes that provide important waterfowl habitat.
Lake residents face big bills for control costs when Brazilian elodea becomes established. Lake Limerick residents in Mason County spend up to $25,000 each year to control this plant. Other lake residents spend similar amounts of money to control Brazilian elodea in their lakes. California has allocated two million dollars in 2000 to manage the problems with Brazilian elodea in the Sacramento-Delta area.
Luckily, there is a good alternative aquarium plant that can be substituted for Brazilian elodea. Canadian elodea or American waterweed (Elodea canadensis) looks very similar to Brazilian elodea and is commonly found in most Washington Lakes. Because it is a native species, American waterweed does not create the same kind of serious problems as Brazilian elodea, although it has been known to become weedy in nutrient-rich waters.
Brazilian elodea and its relatives hydrilla and American waterweed look very similar. Here are some ways to tell these three plants apart: