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Posidonia; Temporal range: Maastrichtian - recent PreꞒ Ꞓ O S D C P T J K Pg N
	Posidonia oceanica
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Monocots
Order:	Alismatales
Family:	Posidoniaceae; Hutch.
Genus:	Posidonia; K.D.Koenig
Type species
	Posidonia oceanica; L.
Species
	See text
	Posidonia distribution range

Posidonia is a genus of flowering plants. It contains nine species of marine plants^[3] ("seagrass"), found in the seas of the Mediterranean and around the south coast of Australia.

The APG system (1998) and APG II system (2003) accept this genus as constituting the sole genus in the family Posidoniaceae, which it places in the order Alismatales, in the clade monocots. The AP-Website^[4] concludes that the three families Cymodoceaceae, Posidoniaceae and Ruppiaceae form a monophyletic group. Earlier systems classified this genus in the family Potamogetonaceae or in the family Posidoniaceae but belonging to order Zosterales.

Posidonia oceanica has nitrogen fixation capabilities via symbiosis and other species may as well.^[5]

Species

This is a list of species that are contained by the genus:^[6]

Posidonia angustifolia Cambridge and Kuo^[7]
Posidonia australis Hook.f. South coast of Australia.
Posidonia coriacea Cambridge and Kuo
Posidonia denhartogii Kuo and Cambridge^[8]
Posidonia kirkmanii Kuo and Cambridge
Posidonia oceanica (L.) Delile – This plant is endemic to the Mediterranean Sea, where it forms undersea meadows.
Posidonia ostenfeldii den Hartog^[9]
Posidonia robertsoniae Kuo and Cambridge
Posidonia sinuosa Cambridge and Kuo

The species described by Linnaeus, Posidonia oceanica, is found in the Mediterranean; the rest are located around the southern coast of Australia. Some species are endemic seagrasses of Western Australia, all the Australian species are found in that region's diverse habitats. This arrangement was divided into two complexes: the Posidonia australis and Posidonia ostenfeldii groups.^[10] Some species descriptions may only be regional characteristics, and may need further revision.^[6]^[11]

In 2006 a clonal colony of P. oceanica was discovered south of the island of Ibiza which measured 8 km across and is possibly up to 100,000 years old.^[12]

Taxonomy

References

^ Aires, T; Marbà, N; Cunha, RL; Kendrick, GA; Walker, DI; Serrão, EA; Duarte, CM; Arnaud-Haond, S (2011-01-17). "Evolutionary history of the seagrass genus Posidonia". Marine Ecology Progress Series. 421. Inter-Research Science Center: 117–130. Bibcode:2011MEPS..421..117A. doi:10.3354/meps08879. ISSN 0171-8630.
^ Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III". Botanical Journal of the Linnean Society. 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. hdl:10654/18083.
^ Christenhusz, M. J. M. & Byng, J. W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. 261 (3). Magnolia Press: 201–217. doi:10.11646/phytotaxa.261.3.1.
^ AP-Website
^ Mohr, Wiebke (3 November 2021). "Terrestrial-type nitrogen-fixing symbiosis between seagrass and a marine bacterium". Nature. 600 (7887): 105–109. Bibcode:2021Natur.600..105M. doi:10.1038/s41586-021-04063-4. PMC 8636270. PMID 34732889.
^ ^a ^b Mike van Keulen. "The genus Posidonia König (nom. cons.) (Posidoniaceae)". Murdoch University.
^ Cambridge, M.L. and Kuo, J. (1979) Two new species of seagrass from Australia, Posidonia sinuosa and Posidonia angustifolia (Posidoniaceae). Aquat. Bot. 6, 307–328 f. Keulen
^ Kuo, J. and Cambridge, M.L. (1984) A taxonomic study of the Posidonia ostenfeldii complex (Posidoniaceae) with descriptions of four new Australian seagrasses. Aquat. Bot. 20, 267–95. f. Keulen
^ den Hartog, C. (1970) Seagrasses of the World. Verh. Kon. Ned. Akad. Wetens. Afd. Naturk. Ser. 2 59:139 f. Keulen
^ Kuo, J. and McComb, A.J. (1989) In: "Biology of Seagrasses. A treatise on the biology of seagrasses with special reference to the Australian region." (Eds. A.W.D. Larkum, A.J. McComb, S.A. Shepherd) (Aquatic Plant Studies 2) (Elsevier, Amsteredam). p. 6-73 f. Keulen
^ Campey, M.L.; Waycott M.; Kendrick G.A. (January 2000). "Re-evaluating species boundaries among members of the Posidonia ostenfeldii species complex (Posidoniaceae) – morphological and genetic variation". Aquatic Botany. 66 (1): 41–56(16) Research article. Bibcode:2000AqBot..66...41C. doi:10.1016/S0304-3770(99)00015-7. Archived from the original on 2020-05-11. Retrieved 2008-11-04.
^ Ibiza Spotlight (28 May 2006). "Ibiza's Monster Marine Plant". Retrieved 2014-08-13.