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'{{short description|Species of plant}} {{Use dmy dates|date=August 2013}} {{use Australian English|date=June 2022}} {{Speciesbox | image = Posidonia australis Spencers Gulf.jpg | status = NT | status_system = IUCN3.1 | status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Short, F.T. |author2=Carruthers, T.J.R. |author3=Waycott, M. |author4=Kendrick, G.A. |author5=Fourqurean, J.W. |author6=Callabine, A. |author7=Kenworthy, W.J. |author8=Dennison, W.C. |date=2010 |title=''Posidonia australis'' |volume=2010 |page=e.T173333A6993340 |doi=10.2305/IUCN.UK.2010-3.RLTS.T173333A6993340.en |access-date=19 November 2021}}</ref> | genus = Posidonia | species = australis | authority = [[Hook.f.]] }} '''''Posidonia australis''''', also known as '''fibre-ball weed''' or '''ribbon weed''', is a species of [[seagrass]] that occurs in the southern waters of Australia. It forms large meadows important to environmental conservation. Balls of decomposing detritus from the foliage are found along nearby shore-lines. ==Description== [[File:Posidonia australis fruits and seed.jpg|thumb|left|From left: immature fruits attached to plant, mature fruit released from plant, splitting fruit ready to release seed, seed]] ''Posidonia australis'' is a flowering plant occurring in dense meadows, or along channels, in white sand. It is found at depths from {{cvt|1-15|m}}. Subsurface [[rhizome]]s and roots provide stability in the sands it occupies. Erect rhizomes and leaves reduce the accumulation of [[silt]]. The leaves are ribbon-like and {{cvt|11–20|mm}} wide. They are bright green, perhaps becoming browned with age.<ref>{{FloraBase|name=''Posidonia australis'' |id=123}}</ref> The terminus of the leaf is rounded or absent through damage. They are arranged in groups with older leaves on the outside, longer and differing in form from the younger leaves they surround. The species is [[monoecious]]. The flowers appear on small spikes on leafless stems, two bracts on each spike. The plant pollinates by [[hydrophily]], by dispersing in the water.<ref name="Keulen">{{Cite web|url=http://www.bsb.murdoch.edu.au/groups/seagrass/posidonia.html|title=The genus ''Posidonia'' König (''nom. cons.'') (Posidoniaceae).|author= Mike van Keulen|publisher=[[Murdoch University]]}}</ref> ''Posidonia australis'' reproduction usually occurs through sexual or asexual methods but, under extreme conditions, by [[pseudovivipary]].<ref>[https://atlasofscience.org/what-happens-when-plant-sex-fails/ Elizabeth Sinclair. What happens when (plant) sex fails? Atlas of Science, 2016]</ref> A 2013 study showed that ''P. australis'' can [[Carbon sequestration|sequester carbon]] 35 times more efficiently than [[rainforests]].<ref>{{cite web|url=http://www.newsroom.uts.edu.au/news/2013/08/humble-plants-may-save-the-planet|archive-url=https://web.archive.org/web/20130819034834/http://www.newsroom.uts.edu.au/news/2013/08/humble-plants-may-save-the-planet|url-status=dead|archive-date=19 August 2013|title=Humble plants may save the planet|work=University of Technology, Sydney|date=14 August 2013|accessdate=15 August 2013}}</ref> <!-- The rhizome type stems are in two forms; growing beneath the sand up to 0.15 m and rising above the sand to give its tufted appearance. All stems are approximately 10 mm thick and upright in habit. This arrangement of the rhizomes eventually forms a [[matte]]; the surface contains the active parts of the plant, whereas the centre is a dense network of roots and decomposing stems. --> ==Distribution== [[File:West Beach wrack.JPG|thumb|Detrital ''P. australis'' accumulation at [[West Beach, South Australia]]]] This species is found in waters around the southern coast of Australia. In [[Western Australia]] is occurs in the [[Shark Bay, Western Australia|Shark Bay]] region, around islands of the [[Houtman Abrolhos]], and southward along the coast of the [[Swan Coastal Plain]]. The species is recorded at the edge of the [[Esperance Plains]], the [[Archipelago of the Recherche]], at the southern coast of the southwest region. The range extends to the east to coastal areas of New South Wales, South Australia, Tasmania, and Victoria.<ref name="Keulen"/> A sign of a nearby occurrence of ''[[Posidonia]]'' is the presence of masses of decomposing leaves on beaches, forming fibrous balls. ==Largest known plant== In June 2022 it was reported that genetic testing had revealed that samples taken from a ''Posidonia australis'' meadow in [[Shark Bay]] up to {{convert|180|km|mi}} apart had revealed that they were all from a single [[Vegetative reproduction|clone]] of the same plant. The plant covers an area of [[seafloor]] of around {{convert|200|km2|mi2}}, which would make it the largest known plant in the world. It is thought to be at least 4,500 years old and grew to this size by using rhizomes to colonise new parts of the seafloor.<ref name="Kilvert 2022">{{cite web | last=Kilvert | first=Nick | title=World's largest plant discovered right under our noses in Western Australia | website=ABC News| publisher= [[Australian Broadcasting Corporation]] | date=1 June 2022 | url=https://www.abc.net.au/news/science/2022-06-01/worlds-largest-plant-seagrass-meadow-shark-bay-giant-clone/101112726 | access-date=1 June 2022}}</ref><ref name="Readfearn 2022">{{cite web | last=Readfearn | first=Graham | title=Scientists discover 'biggest plant on Earth' off Western Australian coast | website=[[The Guardian]] | date=1 June 2022 | url=https://www.theguardian.com/environment/2022/jun/01/what-the-hell-australian-scientists-discover-biggest-plant-on-earth-off-wa-coast | access-date=1 June 2022}}</ref> ==Taxonomy== This species is a member of the family [[Posidoniaceae]], one of eight occurring in Australia. The ninth member, ''[[Posidonia oceanica]]'', is found in the Mediterranean sea. The genus name for this species, ''Posidonia'', is given for the god of the seas [[Poseidon]], and ''australis'' refers to the southern distribution. The species was first described by [[Joseph Dalton Hooker|Joseph Hooker]] in ''[[Flora Tasmaniae]]''.<ref>{{cite journal|author=Hooker, J.D. |date=1858|title=The botany of the Antarctic voyage of H.M. discovery ships Erebus and Terror . III. Flora Tasmaniae|volume= 2|issue=6|page= 43|url=https://www.biodiversitylibrary.org/page/28467228}}</ref> [[Common name]]s for the plant include fibre-ball weed and ribbon weed.<ref name="Readfearn 2022"/> == Conservation status == IUCN lists this species as "near threatened",<ref name="iucn status 19 November 2021" /> while the [[Posidonia australis seagrass meadows of the Manning-Hawkesbury ecoregion|meadows in New South Wales]] have been listed by the [[Commonwealth of Australia]] as an endangered ecological community since 2015.<ref name=sprat>{{cite web|url=https://www.environment.gov.au/cgi-bin/sprat/public/publicshowcommunity.pl?id=127|title=Species Profile and Threats Database: ''Posidonia australis'' seagrass meadows of the Manning-Hawkesbury ecoregion|author=Australian Government|publisher=Department of Agriculture, Water and the Environment}}</ref> ==References== {{Reflist}} ==External links== *[https://avh.ala.org.au/occurrences/search?taxa=Posidonia+australis#tab_mapView ''Posidonia australis'' occurrence data] from [[Australasian Virtual Herbarium]] *{{APNI|name=''Posidonia australis'' |id=2389}} *{{cite journal|url=http://www.publish.csiro.au/paper/PP9840035.htm|title=Posidonia australis Growing in Altered Salinities: Leaf Growth, Regulation of Turgor and the Development of Osmotic Gradients|year=1984 |publisher=[[CSIRO]]|doi=10.1071/pp9840035 |last1=Tyerman |first1=SD |last2=Hatcher |first2=AI |last3=West |first3=RJ |last4=Larkum |first4=AWD |journal=Functional Plant Biology |volume=11 |issue=2 |page=35 }} {{Taxonbar|from=Q3399633}} [[Category:Posidonia|australis]] [[Category:Flora of New South Wales]] [[Category:Flora of South Australia]] [[Category:Flora of Tasmania]] [[Category:Flora of Victoria (Australia)]] [[Category:Angiosperms of Western Australia]] [[Category:Monocots of Australia]]'