Azolla caroliniana is also known as mosquito fern. It is a floating, aquatic fern native to the eastern and southern United States.

It is an extremely hardy plant for the home aquarium and forms large masses in a short time under optimum conditions. The spores of the plant can easily survive cold weather and freezing temperatures. An interesting note is its symbiotic relationship with Anabaena, which are found in small cavities at the base of each leaf. Anabaena is a blue-green algae able to obtain nitrogen from the air and fix it in a way that makes it avaliable for use by its host, A. caroliniana. For this reason, this small floating plant is often grown in rice fields and used as an agricultural fertalizer due to its high nitrogen content.

These are excellent nutrient absorbers and the roots make excellent and attractive cover for fry.