Editing Azolla (section)

==Ecology==
[[File:Azolla-13.3348RGB.tif|alt=Confocal microscopy image of an Azolla filiculoides root cross section showing several layers of cells in a concentric pattern stained in cyan and magenta|thumb|''Azolla filiculoides'' root cross section]]
[[File:Canning rv azolla 10 gnangarra.jpg|thumb|Azolla covering the [[Canning River (Western Australia)]]]]

''Azolla'' is a highly [[plant growth|productive plant]] that can double its [[biomass (ecology)|biomass]] in 1.9 days,<ref>{{cite journal |journal=Aquatic Botany |volume=15 |issue=2 |pages=175–185 |date=1983 |title=The growth of four species of Azolla as affected by temperature |author=Iwao Watanabe, Nilda S.Berja |doi=10.1016/0304-3770(83)90027-X|bibcode=1983AqBot..15..175W }}</ref> depending on growing conditions. The plant can yield can reach 8–10 tonnes fresh matter per hectare in Asian [[paddy field]]s. 37.8 tonnes fresh weight/ha (2.78&nbsp;t/ha dry weight) has been reported for ''A. pinnata'' in India.<ref>{{cite web |title=Hasan, M. R.; Chakrabarti, R., 2009. Use of algae and aquatic macrophytes as feed in small-scale aquaculture: A review. FAO Fisheries and Aquaculture technical paper, 531. FAO, Rome, Italy |url=https://www.fao.org/3/i1141e/i1141e00.htm |website=fao.org/ |access-date=18 August 2014}}</ref>

''Azolla'' floats on the surface of water by means of numerous small, closely overlapping scale-like [[Leaf|leaves]], with their roots hanging in the water. They form a [[symbiosis|symbiotic]] relationship with the [[cyanobacterium]] ''[[Anabaena|Anabaena azollae]]'',{{refn|1=Currently ''[https://lpsn.dsmz.de/species/trichormus-azollae Trichormus azollae]'' {{au|(Strasburger 1884) Komárek and Anagnostidis 1989}}. Synonyms: ''Nostoc azollae'' {{au|Strasburger 1883}}, ''Anabaena azollae'' {{au|Strasburger 1884}}, ''Desikacharya azollae'' {{au|(Strasburger 1884) Saraf et al. 2019}}.{{cn|date=January 2025}}|group=note}} which lives outside the cells of its host and which [[nitrogen fixation|fixes]] [[atmospheric]] [[nitrogen]].<ref>{{cite journal | pmc=2900214 | year=2010 | last1=Ran | first1=L. | last2=Larsson | first2=J. | last3=Vigil-Stenman | first3=T. | last4=Nylander | first4=J. A. | last5=Ininbergs | first5=K. | last6=Zheng | first6=W. W. | last7=Lapidus | first7=A. | last8=Lowry | first8=S. | last9=Haselkorn | first9=R. | last10=Bergman | first10=B. | title=Genome Erosion in a Nitrogen-Fixing Vertically Transmitted Endosymbiotic Multicellular Cyanobacterium | journal=PLOS ONE | volume=5 | issue=7 | pages=e11486 | doi=10.1371/journal.pone.0011486 | pmid=20628610 | bibcode=2010PLoSO...511486R | doi-access=free }}</ref> 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. Unlike all other known plants, its symbiotic microorganism [[Vertical transmission|transfers directly]] from one generation to the next. ''A.&nbsp;azollae'' is completely dependent on its host, as several of its genes have either been lost or transferred to the [[cell nucleus|nucleus]] in Azolla's cells.<ref>{{Cite web|url=https://www.geolsoc.org.uk/Geoscientist/Archive/June-2014/The-Arctic-Azolla-event|title=The Geological Society of London - The Arctic Azolla event|website=www.geolsoc.org.uk}}</ref>

The nitrogen-fixing capability of ''Azolla'' has led to widespread use as a [[biofertiliser]], especially in parts of [[southeast Asia]]. The plant has been used to bolster agricultural productivity in China for over a thousand years. When [[paddy field|rice paddies]] are flooded in the spring, they can be planted with ''Azolla'', which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material resulting from the die-off of this ''Azolla'' releases nitrogen into the water for the rice plants, providing up to nine tonnes of [[protein]] per hectare per year.<ref>{{Cite web|url=http://www.fao.org/ag/AGA/AGAP/FRG/afris/DATA/558.htm|title=FAO figures}}</ref>

''Azolla'' are [[weed]]s in many parts of the world, entirely covering some bodies of water. The myth that no [[mosquito]] can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern";<ref name="Mosquito Fern">{{cite web |url=http://www.americaswetlandresources.com/wildlife_ecology/plants_animals_ecology/plants/mosquitofern.html |title=Mosquito Fern |access-date=2007-11-10 |work=America's Wetland Resource Center |publisher=Loyola University, New Orleans |archive-date=May 16, 2006 |archive-url=https://web.archive.org/web/20060516014940/http://www.americaswetlandresources.com/wildlife_ecology/plants_animals_ecology/plants/mosquitofern.html |url-status=dead }}</ref> however, ''Azolla'' may deter the survival of some of mosquito larvae.<ref name=":0" />

Most species can produce large amounts of [[3-deoxyanthocyanin|deoxyanthocyanin]]s in response to various stresses,<ref>{{cite journal |doi=10.1007/BF02857915 |last1=Wagner |first1=G.M. |year=1997 |title=''Azolla'': a review of its biology and utilization |journal=Bot. Rev. |volume=63 |issue=1 |pages=1–26 |bibcode=1997BotRv..63....1W |s2cid=347780}}</ref> including bright sunlight and extreme temperatures,<ref>{{cite journal |doi=10.1007/BF02859886 |last1=Moore |first1=A. W. |year=1969 |title=''Azolla'': Biology and agronomic significance |journal=Bot. Rev. |volume=35 |issue=1 |pages=17–35 |bibcode=1969BotRv..35...17M |s2cid=42431293}}</ref><ref>{{cite journal |last1=Zimmerman |first1=William J. |year=1985 |title=Biomass and Pigment Production in Three Isolates of ''Azolla'' II. Response to Light and Temperature Stress |journal=Ann. Bot. |volume=56 |issue=5 |pages=701–709 |doi=10.1093/oxfordjournals.aob.a087059}}</ref> causing the water surface to appear to be covered with an intensely red carpet. [[Herbivore]] feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of [[polyunsaturated fat]]ty acids in the [[fronds]], thus lowering their palatability and nutritive value.<ref>{{cite journal |doi=10.1016/S0304-3770(02)00077-3 |last1=Cohen |first1=M.F. |last2=Meziane |first2=T. |last3=Tsuchiya |first3=M. |last4=Yamasaki |first4=H. |year=2002 |title=Feeding deterrence of ''Azolla'' in relation to deoxyanthocyanin and fatty acid composition |url=http://www.bashanfoundation.org/michael/michaelfeeding.pdf |journal=Aquatic Botany |volume=74 |issue=2 |pages=181–187 |bibcode=2002AqBot..74..181C |access-date=2010-01-22 |archive-url=https://web.archive.org/web/20081122000150/http://www.bashanfoundation.org/michael/michaelfeeding.pdf |archive-date=2008-11-22 |url-status=dead}}</ref>

''Azolla'' cannot survive winters with prolonged freezing, so is often grown as an [[ornamental plant]] at high latitudes where it cannot establish itself firmly enough to become a weed. It is also not tolerant of [[salinity]]; normal plants cannot survive in greater than 1–1.6‰, and even conditioned organisms die if grown in water with a salinity above 5.5‰.<ref name=Brinkhuis2006>{{cite journal
|author=Brinkhuis, H.
|author2=Schouten, S.|author3=Collinson, M.E.|author4=Sluijs, A.|author5=Sinninghe Damsté, J.S.|author6=Dickens, G.R.|author7=Huber, M.|author8=Cronin, T.M.|author9=Onodera, J.|author10=Takahashi, K.
|year=2006
|title=Episodic fresh surface waters in the Eocene Arctic Ocean
|journal=Nature
|volume=441
|pages=606–9
|url=http://www.nature.com/search/executeSearch?sp-q-9=NATURE&sp-q=Episodic+fresh+surface+waters+in+the+Eocene+Arctic+Ocean&sp-c=10&sp-x-9=cat&sp-s=date&submit=go&sp-a=sp1001702d&sp-sfvl-field=subject%7Cujournal&sp-x-1=ujournal&sp-p-1=phrase&sp-p=all
|access-date=2007-10-17
|doi=10.1038/nature04692
|pmid=16752440
|issue=7093
|bibcode=2006Natur.441..606B|display-authors=etal|hdl=11250/174278|s2cid=4412107|hdl-access=free}}</ref><ref name="Speelman-2009"/>

===''Azolla filiculoides''===
''Azolla filiculoides'' (red azolla) is the only member of the family Azollaceae found in [[Tasmania]], where it is a common native aquatic plant. It is often found behind farm dams and other still waterbodies. The plants are small (usually only a few cm across) and float, but they are fast growing, and can be abundant and form large mats. The plants are typically red, and have small, water repellent leaves.