View source for Azolla

{{SPlantbox
|genus=Azolla
|Temp Metric=°F
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{{Inc|
Azolla (Greek, to destroy by drying). Salviniaceae. A small genus of floating aquatics with small, pinnately branched sts. and minute fleshy 2-lobed lvs., producing 2 sorts of spores in globular sporocarps. The plants multiply rapidly by self-division, and will grow readily in water containing a little nutriment. The species are distinguishable only by microscopic examination. In natural conditions, the plants grow so closely together and multiply so rapidly as to cover very completely any quiet water surface. For this reason, they have been found useful in preventing the propagation of mosquitos in Germany and Panama.
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{{Taxobox
| color = lightgreen
| name = Mosquito fern
| image = Azolla caroliniana0.jpg
| image_width = 200px
| image_caption = ''Azolla caroliniana''
| regnum = [[Plant]]ae
| divisio = [[fern|Pteridophyta]]
| classis = [[Pteridopsida]]
| ordo = [[Salviniales]]
| familia = '''Azollaceae'''
| familia_authority = [[Richard Wettstein|Wettst.]]
| genus = '''''Azolla'''''
| genus_authority = [[Jean-Baptiste Lamarck|Lam.]]
| subdivision_ranks = Species
| subdivision = 
''[[Azolla caroliniana]]'' <small>Willd.</small><br/>
''[[Azolla filiculoides]]'' <small>Lam.</small><br/>
''[[Azolla japonica]]'' <small>Franch. & Sav.</small><br/>
''[[Azolla mexicana]]'' <small>Presl</small><br/>
''[[Azolla microphylla]]'' <small>Kaulf.</small><br/>
''[[Azolla nilotica]]'' <small>Decne. ex Mett.</small><br/>
''[[Azolla pinnata]]'' <small>R.Br.</small>
}}

'''''Azolla''''' ('''mosquito fern''', '''duckweed fern''', '''fairy moss''', '''water fern''') is a [[genus]] of seven species of [[aquatic plant|aquatic]] [[fern]]s, the only genus in the family '''Azollaceae'''. They are extremely reduced in form and specialized, looking nothing like conventional ferns but more resembling [[duckweed]] or some [[moss]]es.

They float 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 [[symbiosis|symbiotic]] relationship with the [[cyanobacterium]] ''[[Anabaena|Anabaena azollae]]'', which allows the plants to [[nitrogen fixation|fix nitrogen]] from the [[air]].

[[Image:Azolla01.jpg|thumb|left|SEM image of Azolla surface]]
Because of their nitrogen-fixing capability, they have enabled an increase in agricultural productivity in parts of southeast [[Asia]]. When [[rice]] paddies are flooded in the spring, they can be inoculated with ''Azolla'', which then quickly multiplies to cover the water, suppressing weeds. As the plants die, they contribute [[nitrogen]] to the rice plants, and as the rice paddy dries out, the ''Azolla'' all eventually die, making an exceptional [[green manure]], providing up to nine tonnes of protein per hectare per year [http://www.fao.org/ag/AGA/AGAP/FRG/afris/DATA/558.htm FAO figures]. As such, ''Azolla'' may be used in place of agrochemicals.

''Azolla'' are also serious [[weed]]s in many parts of the world, covering bodies of water so thickly that no water is exposed. This is where they derive the name 'mosquito fern', from the belief that no [[mosquito]] can penetrate the coating of fern to lay its [[Egg (biology)|egg]]s in the water{{Fact|date=February 2007}}. ''Azolla'' is reputed to be able to grow so quickly that it can double its mass in three days under good conditions.

Most of the species can produce large amounts of [[anthocyanin]]s in bright sunlight, creating an intense red color and causing the water surface to appear to be covered with a red carpet.

Mosquito ferns are safe to grow in cool temperate areas with prolonged freezing in winter, as they cannot overwinter in these conditions. They are often grown as an [[ornamental plant]] by [[water garden|water-garden]] hobbyists.