Common name: 
Mosquito fern
Edibility: 
1 - famine food
Notes: 

Azolla is a floating water fern that has a symbiotic relationship with a nitrogen-fixing bacteria. It floats on the surface of water by means of numerous, small, closely-overlapping scale-like leaves, with their roots hanging in the water. It can produce large amounts of anthocyanins in bright sunlight, creating an intense red color and causing the water surface to appear to be covered with a red carpet. Azolla can reproduce asexualy by breaking off. Each branch that breaks off forms a new plant. Azolla can also reproduce sexually. Like all ferns, Azolla produce spores.

Azolla has reportedly been used as a feed for pigs and ducks in SE Asia; for cattle, fish and poultry in Vietnam; and for pigs in Singapore and Taiwan. It is described as an excellent substitute for green forage for cattle in Vietnam and may replace up to 50% of the rice bran used as feed for pigs in that country. Although very low in DM, it contains a high level of protein (24% CP). The amino acid composition of Azolla compared well with reference protein sources.

Azolla has been used as a green manure crop in Vietnam and China for centuries. The ability of azolla to shade out weeds in wetland rice and taro has been noted by farmers and researchers since the early 20th century.

Azolla caroliniana
Cultivation: 

In tropical Asia azolla is traditionally cultivated as a green manure for rice in two ways. One way is to set aside 5-10% of the crop area for year-round production. The cultivated azolla is later added to crop fields as compost. In the second way, azolla is cultivated in the rice fields and incorporated before and/or after the rice crop and between crops. Ideally azolla is grown several times before rice transplanting. When azolla is used to suppress weeds in rice or taro production a rate of 0.5kg/m2 is used. Azolla is propagated in the field for 2-4 weeks prior to transplanting (depending on azolla growth rates which are generally higher in summer and lower in winter in Hawai`i).

Propagation: 
Azolla is almost always propagated vegetatively since its most common mode of multiplication is vegetative. Like other ferns, it produces spores, not seeds. When a frond reaches a certain size, the older stems detach themselves from the main stem as a result of the formation of an abscission layer.