Elodea, sometimes called anacharis, is the Latin name for a family of water weeds often used in aquariums and ponds. These plants can escape into the wild and some variants are considered an invasive species. They provide a useful habitat for small fish and crustaceans, but because they propagate by breaking off and floating away, they can often choke up a pond.
The Elodea genus is part of the water weed species and grows underwater with its flowers breaking the surface. The name elodea means “of marshes” and there are roughly 12 types of elodea.
The most well-known type of elodea is Canadian or American water weed or pond weed, Elodea canadensis. Elodea grows in fresh water all over the world.
The elodea is a rooted plant. It has a long, slender stalk filled with clusters of finely-toothed leaves. The number of leaves per cluster varies from about three to eight depending on type of elodea; the color is usually bright to dark green. Flowers are one-half to one inch across and white, on short stems; the plant grows as long as it needs to put its flowers above water.
The elodea's fruits are cylindrical or oval and after overwintering the plant develops its own “cuttings,” essentially breaking off stalks full of leaves to float off and plant elsewhere.
Elodea is very adept at colonization and its ability to self-cut means that some species like Elodea canadensis, Elodea crispa and Elodea nuttallii are considered noxious weeds.
While not actually part of the Elodea genus, Brazilian elodea (Egeria densa) is related. This plant creates thick mats that choke waterways and create problems of flow, silting and even block people's ability to perform water sports. Egeria densa was formerly classified as Elodea, hence its common name, but was reclassified due to differences in the way its leaves grow on the stem.
Elodea are often sold in nurseries and pet shops for pond use, then escape into the wild, though some states such as Texas and Washington have outlawed the sale of certain species.
Elodea are used for aquarium plants, giving the fish somewhere to hide. Science teachers can demonstrate the plants' use of carbon dioxide by using bromothymol blue.
In the wild, elodea also create useful hiding places for fish and other aquatic animals as well as food for crustaceans.
In areas where elodea has become a problem, control methods vary. According to the AquaPlant section of the Texas Agrilife Extension Service website, areas can be covered physically or with dyes to block out the light and herbicides like fluridone can also be used.
Elodea can be harvested though chopping them up tends to make them spread because of their propagation method. Triploid grass carp eat Brazilian elodea and have been used in control.