The tiniest fern in the world is alive and well in New Orleans! The Mosquito Fern (Azolla carolinensis) is a small floating species that may cover the surface of still waters much as duck weed (locally known as peanut grass) does. It is olive green in spring and early summer and changes to a rusty hue by mid-summer, thus causing the surface of roadside ditches to appear red.
The name Mosquito Fern derives from the belief that mosquitoes cannot lay their eggs in water covered by the diminutive plants.
Mosquito Fern does not fill a normal fern niche and its 32nd of an inch wide overlapping leaflets are not impressive, but this tiny plant is important in the food market of many undeveloped countries. Each leaflet has a pouch which contains a symbiotic blue-green alga (Anabaena azollae) which converts atmospheric nitrogen to a form which can be used by other plants. The fern uses a portion of the nitrogen as it becomes available and when the plant dies and settles to the bottom, it releases the remaining nitrogen for use by other organisms. A good example of human application of this phenomenon is that rice paddies in southeast Asia may be covered with Mosquito Fern during the early growing season, producing as much as 40 lb of nitrogen per acre. As the rice grows and shades the ferns, they die and sink to the bottom, thus recycling the vital nutrient to the food crop. Commercial fertilizers are produced at great expense and are virtually unavailable to undeveloped countries. The Mosquito Fern is one of Mother Nature’s natural sources of cost-free fertilizer.