Azolla pinnata, commonly known as mosquitofern or water velvet, is a small, free-floating aquatic fern native to warm-temperate and tropical regions of Africa, Asia, and parts of Australia. It thrives in still or slow-moving freshwater bodies such as ponds, ditches, and wetlands. This fern forms dense mats on the water surface, which can be green to reddish depending on nutrient levels and light exposure. Mosquitofern is notable for its symbiotic relationship with the cyanobacterium Anabaena azollae, which resides in cavities within the leaves and fixes atmospheric nitrogen, enriching the water with nutrients.

Azolla pinnata is valued for its ability to quickly cover water surfaces, which can help reduce the proliferation of mosquito larvae, hence the common name "mosquitofern." It is also used as a green manure in rice paddies due to its nitrogen-fixing capabilities, improving soil fertility. In ornamental water gardens, it can provide a unique texture and color contrast. However, care must be taken as it can become overly abundant and potentially invasive, blocking sunlight and outcompeting native aquatic plants. It prefers nutrient-rich waters and can tolerate a range of pH levels. While it can grow in partial shade, full sun encourages the most vigorous growth.CC BY-SA 4.0