feathered mosquitofern

Azolla pinnata, commonly called feathered mosquito fern or ferny azolla, is a small floating fern distributed across tropical and warm-temperate regions of Asia, Africa, Madagascar, and Australia, where it forms dense green to reddish mats on the surface of stagnant nutrient-rich waters such as ponds, rice paddies, and drainage ditches. The plant has a long history of agricultural use as green manure in Asian rice paddies, thanks to its symbiotic relationship with nitrogen-fixing cyanobacteria that live in cavities on the underside of its leaves — a trait shared with all members of the genus Azolla. The fronds are small, reaching 1 to 2 cm across, and are composed of tiny overlapping scales that give the plant a moss-like or ferny texture. In an aquarium, Azolla pinnata serves as an efficient nutrient export plant, absorbing excess nitrogen and phosphates directly from the water column through its roots. It requires medium to strong light and benefits from elevated nutrient levels; in low light the fronds pale and growth stalls. CO2 injection is not necessary — the plant obtains carbon from the air. Under optimal conditions it grows quickly between 20 and 30°C. At higher temperatures the plant may slow down; it can survive brief periods outside this range but will not thrive. Outdoor ponds are an ideal setting, where it competes vigorously with duckweed. Propagation is passive — daughter plants separate from the parent and any fragment that breaks off grows into a new plant. Regular skimming is necessary to prevent it from covering the entire surface and blocking light to submerged plants.