Azolla caroliniana

Eastern mosquito fern is a native annual aquatic plant in the Water-fern family (Salviniaceae). It is widespread in eastern North American and northern South America, growing in still or very slow-moving water, shallow ponds, ditches and sluggish streams.  

It grows in partial to full sun, in permanent standing water. To propagate this plant, move divisions of it to a new area. To keep it alive when temperatures dip, overwinter it indoors.

The delicate, lacey, scale-like leaves overlap and float on the water’s surface forming a dense mat with the roots trailing below the surface. New leaves are a bright green or gray green and can fade to rusty red especially if grown in bright conditions. The leaflets house a symbiotic blue-green alga (Anabaena azollae) that fixes nitrogen. This very short plant grows less than 1 inch tall but can break off and form a mat that covers the water’s surface very quickly making it difficult for mosquitos to deposit their eggs, hence the common name "mosquito fern." Another explanation is that this fern is associated with mosquitoes, as they both favor similar environments.

Use it in water gardens, ponds or aquaria. The leaves are normally not eaten by fish. It is a rapidly growing and spreading aquatic plant, which may affect the location chosen for its use.

Insects, Diseases, and Other Plant Problems:  No serious problems.