Azolla is a genus of seven species of aquatic ferns. They are also known as: Mosquito fern, Duckweed fern, Fairy moss, and Water fern.

Azollas live in ponds, lakes, swamps, and streams in both tropical and sub-tropical conditions. They have a short, branched, floating stem, and roots that hang down in the water. The leaves are alternately arranged, each consisting of a thick aerial dorsal lobe containing green chlorophyll and a slightly larger thin, colourless, floating ventral lobe.

Azollas are the only known pteridophyte that lives in symbiosis with a diazotrophic cyanobacterium. All the species of the genus harbor in their fronds a filamentous N2-fixing cyanobacterium until now referred as Anabaena azollae (Nostocaceae).    

Azollas have been used in southern China and northern Vietnam as green manure for rice for many centuries. They can also be supplemented with regular feed of the animal @ 2-2.5 kg of azolla per animal