| Mosquito ferns, Azolla pinnata, Anabaena azollae, Salvinia, Lemna|
Azolla caroliniana, the Carolina mosquitofern, Carolina azolla, or water velvet, is a species of Azolla native to the Americas, in eastern North America from southern Ontario southward, and from the east coast west to Wisconsin and Texas, and in the Caribbean, and in Central and South America from southeastern Mexico (Chiapas) south to northern Argentina and Uruguay.
It is a freshwater aquatic fern, with scale-like fronds 5–10 mm long, green to reddish, most often reddish in strong light and in winter. They are covered in fine hairs that give it the appearance of velvet. It is able to fix nitrogen from the air by means of symbiotic cyanobacteria. It can survive winter water temperatures of 5 °C, with optimum summer growth between 25–30 °C.
Azolla caroliniana Wikipedia
Azolla caroliniana is of commercial importance in cultivation in southern and eastern Asia as a bio-fertilizer, valued for its nitrogen-fixing ability, which benefits crops such as rice when the fern is grown under it and reduces the need for artificial fertilizer addition. The thick mat of fronds (up to 4 cm thick) also suppresses weed growth. Harvested fronds are also used as a food for fish and poultry. It is also often used as a floating plant in both coldwater and tropical aquaria, as well as in outdoor ponds; it is propagated by division.