Azolla is a unique freshwater fern that is one of the fastest growing plants on the planet due to its symbiotic relationship with a cyanobacterium (‘blue-green alga’) called Anabaena. Anabaena draws down the atmospheric nitrogen that fertilizes Azolla, and Azolla provides a nitrogen-filled home for Anabaena within its leaf cavities. This enables the plant to double its biomass in as little as two days free floating on water as shallow as one inch (2.4 cm).
Azolla‘s rapid growth makes it a potentially important sequester of the greenhouse gas carbon dioxide which is converted directly into Azolla‘s biomass. This provides local livestock feed, biofertilizer and biofuel wherever Azolla is grown, so that this remarkable plant has the potential to help us weather the Perfect Storm – the related threats of man-made climate change and shortages of food and land as our population passes seven billion.
Why is Azolla Unique?
Azolla is unique because it is one of the fastest growing plants on the planet – yet it does not need any soil to grow. Unlike almost all other plants, Azolla is able to get its nitrogen fertilizer directly from the atmosphere. That means that it is able to produce biofertilizer, livestock feed, food and biofuel exactly where they are needed and, at the same time, draw down large amounts of CO2 from the atmosphere, thus helping to reduce the threat of climate change.
How is it able to do this?
Azolla and Anabaena – the Perfect Marriage
Each partner gives something to the other in this Perfect Marriage. Because oxygen is poisonous to cyanobacteria, Azolla provides an oxygen-free environment for Anabaena within its leaves. In return, Anabaena sequesters nitrogen directly from the atmosphere which then becomes available for Azolla’s growth, freeing it from the soil that is needed by most other land plants for their nitrogen fertilization.
The oldest Azolla fossils are more than 70 million years old, representing the remains of plants that lived during the Late Cretaceous Period when dinosaurs roamed the earth. They occur in sediments that were deposited in quiescent freshwater bodies, such as lakes, ponds and sluggish rivers, identical to those inhabited by modern Azolla.
- Fossil Azolla (left) has leaves (circled above in red) and tendrils (circled in blue) that are identical to those of modern Azolla (right). The fossil is from the Green River Formation of Colorado, dated between 50.5 and 55.5 million years. The photograph was kindly provided by Dr Ian Miller of the Denver Museum of Nature and Science.
Several other symbioses are known between plants and cyanobacteria – for example in legumes – but the Azolla-Anabaena relationship is the only known symbiosis in which a cyanobacterium passes directly to subsequent generations via the plant’s reproductive sporangia and spores.
So Azolla and Anabaena have never been apart for 70 million years. During that Immense period of time, the two partners have co-evolved numerous complementary ways that make them increasingly efficient.
The Azolla Superorganism: A unique biological system
In 2010, our Associate Francisco Carrapiço proposed that Azolla-Anabaena should be designated as a superorganism “because of its unique symbiosis in which the two partners have successful co-evolved into a system that makes important contributions to ecology, biofertilization and biotechnology” (Carrapiço, 2010).
The challenge, then, is to work with Azolla and use its remarkable properties to help us weather the Perfect Storm that now threatens us and the other species with whom we share our planet.
You can find more details about Azolla, its history, and its multiple uses on our information website The Azolla Foundation.