Azolla filiculoides (Mosquito Fern) is a tiny free-floating fern forming a mat of pinnately branched stems covered with minute, two-lobed leaves arranged in two rows. The upper leaf floats on the surface and the lower leaf is submerged. The bright green foliage turns purplish-rose in response to stress such as very bright light or very high or low temperatures. Small feather-like roots are produced along the lower surface of the stem and hang freely in the water. Nutrients are absorbed directly from the water by the roots. Native to both North and South America, Mosquito Fern occurs naturally in ponds and lakes, in slow-moving streams and rivers. It grows extremely quickly under optimum conditions and can sometimes become a nuisance. It can form thick mats that completely cover the surface of the water, preventing mosquitoes from depositing their eggs. It also discourages algae growth and helps keep waters clear. Mosquito Fern is cultivated as an ornamental plant for use in water gardens, aquaria, and ponds.

• Grows up to 3 in. tall (7 cm) and spreads indefinitely.
• Performs best in full sun to part shade in water gardens, ponds, or aquatic containers.
• Virtually pest and disease free.
• Reduce its spread by removing portions with a net.
• Azolla filiculoides can grow quickly, easily out-competing indigenous vegetation. Decaying root and leaf matter below a mat of Azolla filiculoides, coupled with the lack of light penetration, can create an anaerobic environment which can reduce the quality of drinking water and make survival for other organisms in the water impossible.
• Propagate by redistributing clusters of plantlets when they appear.
• Native to the Rocky Mountain states of the western USA and Canada, through Central America, and to most of South America. It has been introduced to Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean, and Hawaii.