Egeria is a genus of aquatic plants native to the warm and temperate regions of South America. The two species in this genus are known by names like Brazilian waterweed, Anacharis, and Elodea. Historically, these plants were made widely available by the aquarium trade, but because both species are highly invasive, many regions have limited the sale of these plants to reduce the risk of damage to the natural environment. People interested in cultivating these plants may be able to obtain plants in their region, or can see if other aquarists have cuttings available.
Both species of Egeria have lance-shaped leaves arranged in whorls of four around the stem. The plants have long, trailing stems and produce white flowers periodically. The underwater sections of the plant can provide a source of food and habitat to aquatic organisms while the sections that float above the surface allow the plants to cross-pollinate with each other.
These plants require warm to temperate water and do not do well in extremely hot or cold conditions. Egeria can be grown from cuttings or seeds. It grows very rapidly and can quickly colonize an area of water, unless it is controlled by people or natural predators. Within its native range, animals and other plants usually keep populations of Egeria in check and prevent the plant from becoming invasive. Outside South America, Egeria becomes invasive as a result of having no natural predators.
Commonly, Egeria is introduced to waterways when aquarists dump unwanted fish and plants. If the water is warm, the plant will thrive, and can start spreading rapidly. As boaters and animals move through the area, they can pick up plants and carry them to regions where it has not yet settled. Controlling this plant when it becomes invasive is challenging, as it may be necessary to limit usage of infested waterways in addition to introducing pests to prey on the plants, and the introduction of predators can potentially create another invasive species problem.
Aquarium suppliers and garden supply stores with aquatic plants may be able to provide people with alternatives to Egeria for their aquariums and water gardens. There are a number of aquatic plants with similar growth habits that are safe for use with a variety of fish and other plants. People with existing Egeria in their tanks should be careful about how the plant is disposed of when they remove excess growth or clean out a tank.