Egeria densa is one of the fastest growing, and most commonly available plants in the aquarium hobby. Unfortunately, it is also one of the most frequently released, and has become established, along with Hydrilla, as one of the most invasive nuisance plants all over the world. It masquerades as all three common names, and before keeping it in your tanks you should make sure that it is not illegal in your state. The main reason the egeria/elodea/anachris is such a problem in lakes and streams is that it is an extremely adaptable plant that will grow in almost any conditions of light, nutrients, pH and hardness. This plant will keep growing and swirling on the water surface if left uncut. It does make an excellent aquarium plant as it is easy to keep and easy to propagate. There are what appear to be a few different varieties, but they are really only different forms of the same plant, depending on the light and nutrients available.