Below are excerpts about Azolla from Wikipedia, edited for brevity.
Azolla is a very common native aquatic plant. The plants are small (usually only a few cm across) and float, but can be very abundant and form large mats. Azolla floats on the surface of water by means of numerous, small, closely overlapping scale-like leaves, with their roots hanging in the water. They form a symbiotic relationship with the cyanobacterium Anabaena azollae, which fixes atmospheric nitrogen, giving the plant access to the essential nutrient. This has led to the plant being dubbed a “super-plant”, as it can readily colonize areas of freshwater, and grow at great speed – doubling its biomass every two to three days. The nitrogen-fixing capability of Azolla has led to Azolla being widely used as a biofertilizer, especially in parts of southeast Asia.
Indeed, the plant has been used to bolster agricultural productivity in China for over a thousand years. When rice paddies are flooded in the spring, they can be inoculated with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material releases nitrogen to the rice plants, providing up to nine tons of protein per hectare per year.The myth that no mosquito can penetrate the coating of fern to lay its eggs in the water gives the plant its common name “mosquito fern”.Most Azolla species can produce large amounts of deoxyanthocyanins in response to various stresses,including bright sunlight and extremes of temperature, causing the water surface to appear to be covered with an intensely red carpet.
Azolla is finding increasing use for sustainable production of livestock feed.Azolla is rich in proteins, essential amino acids, vitamins and minerals. Studies describe feeding Azolla to dairy cattle, pigs, ducks, and chickens, with reported increases in milk production, weight of broiler chickens and egg production of layers, as compared to conventional feed. Azolla has also been suggested as a food stuff for human consumption. However, no long term studies of the healthiness of eating Azolla have been made on humans.