Azolla

Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more resembling duckweed or some mosses. Azolla filiculoides is one of just two fern species for which a reference genome has been published. It is believed that this genus grew so prolifically during the Eocene (and thus absorbed such a large amount of carbon) that it triggered a global cooling event that has lasted to the present. Azolla is considered an invasive plant in wetlands, freshwater lakes and ditches . It can alter aquatic ecosystems and biodiversity substantially. Phylogeny of Azolla Other species include: At least six extinct species are known from the fossil record: Azolla intertrappea Sahni & H.S. Rao, 1934 (Eocene, India) Azolla berryi Brown, 1934 (Eocene, Green River Formation, Wyoming) Azolla prisca Chandler & Reid, 1926 (Oligocene, London Clay, Isle of Wight) Azolla tertiaria Berry, 1927 (Pliocene, Esmeralda Formation, Nevada) Azolla primaeva (Penhallow) Arnold, 1955 (Eocene, Allenby Formation, British Columbia) Azolla boliviensis Vajda & McLoughlin, 2005 (Maastrichtian - Paleocene, Eslaboacuten Formation and Flora Formation Bolivia) Azolla is a highly productive plant. It can double its biomass in as little as 1.9 days, depending on growing conditions, and yield can reach 8–10 tonnes fresh matter/ha in Asian rice fields. 37.8 t fresh weight/ha (2.78 t DM/ha dry weight) has been reported for Azolla pinnata in India (Hasan et al., 2009). 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, an extracellular endosymbiont (living outside the host's cells) which fixes atmospheric nitrogen. The typical limiting factor on its growth is phosphorus; thus, an abundance of phosphorus - due for example to eutrophication or chemical runoff - often leads to Azolla blooms.