Azolla filiculoides (Großer Algenfarn)

The water fern is a very compact yet fast-growing aquatic plant native to North America, but it has since become established as an introduced species in Europe, South Africa, and Asia.

It belongs to the family of floating ferns (Salviniaceae), but the individual plants remain significantly smaller than those of its close relatives, the true floating ferns of the genus Salvinia.

Under good conditions, Azolla grows very quickly. This is also due to the fact that it lives in symbiosis with the cyanobacterium Anabaena azollae, which can fix nitrogen from the air.

With plenty of light, it turns an intense dark red, but this is almost only achievable when kept outdoors, where ample light and cool nighttime temperatures promote this coloration.