Azolla Fact Sheet

Azolla is a very small floating fern.  It will only grow in fresh water and does not tolerate a lot of salt.  In good conditions in summer it can grow at an astonishing rate, doubling its size in a few days.  Some people confuse it with duckweed.  When plants are very small they may have a slight superficial resemblance to duckweed, but they are not closely related.  Duckweed is technically a flowering plant (although its flowers are very rarely seen) while Azolla is a fern.  Azolla reproduces by fragmentation.  It can also reproduce by spores like most ferns and this may explain why it sometimes appears in water previously free of it.  Azolla is very widespread round the world.

Duckweed grows best in high nutrient conditions which have to include nitrogen.  Azolla is slightly different in growing even in the absence of fixed Nitrogen, although it does require enough Phosphorous.  Azolla is actually a symbiotic entity made up of a fern and a filamentous blue green alga. The Alga fixes atmospheric nitrogen which is available to both partners in the relationship.  The fossil record suggests that Azolla has been around for at least 80 million years in its present form.

In parts of Asia, Azolla is grown as a green manure crop before a rice harvest and greatly improves the yield of the rice.  Azolla taken from a garden pond is a useful plant to compost.  Azolla can be fed at low levels to egg laying poultry and can increase their egg production.  Like many water plants Azolla has a high water content.  Of the dry matter in Azolla, tests suggest a crude protein level of between 18 and 32 percent.

Azolla can grow so well that it can be a problem.  A thick mat of Azolla makes it difficult for mosquito larvae to breathe.   Fish will eat it and also the tiny animals that grow on and around it.  In a pond it can greatly reduce the amount of algae, but will also make it very difficult for plants to grow underwater.