Azolla filiculoides

The only sure method of distinguishing this species from A. cristata (long incorrectly known as A. caroliniana) is to examine the trichomes on the upper surfaces of the leaves. Trichomes are small protuberances that create water resistance. They are unicellular in A. filiculoides but septate (two-celled) in A. cristata. ==Cultivation==

The species has been introduced to many regions of the Old World, grown for its nitrogen-fixing ability that may be used to enhance the growth rate of crops grown in water, such as rice, or by removal from lakes for use as green manure. A. filiculoides is frequently cultivated in aquariums and ponds, where it can become easily dominant over other species. ==Invasive species==

A. filiculoides was first recorded in Europe in 1870s–1880s, when the species may have been accidentally transported in ballast water, with fry, or directly as an ornamental or aquarium plant. It was introduced into Asia from East Germany in 1977 as an alternative to the cold susceptible native strain of A. pinnata, used as a green manure in the rice industry. A. filiculoides has also been spread around the world as a research model plant for the study of Azolla–Anabaena symbiosis. In the areas of introduction, A. filiculoides is capable of rapid growth, especially in eutrophic ecosystems, and outcompetes native aquatic plants. The dense mat of A. filiculoides causes lack of light penetration and an anaerobic environment due to detritus decomposition, causing a drastic reduction of water quality, aquatic biodiversity, and ecosystem function. ==See also==

Azolla filiculoides0.jpg|Close-up of a leaf Image-IMG 0018Afil.JPG|A. filiculoides (pink-tinged) with Lemna minor AzollaFiliculoidesProfilDetail.jpg|Single A. filiculoides plant showing the roots ==References==