TheAPG system (1998) andAPG II system (2003) accept this genus as constituting the sole genus in the familyPosidoniaceae, which it places in the orderAlismatales, in the clademonocots. The AP-Website[5] concludes that the three familiesCymodoceaceae, Posidoniaceae andRuppiaceae form a monophyletic group. Earlier systems classified this genus in the familyPotamogetonaceae or in the family Posidoniaceae but belonging to orderZosterales.
Posidonia oceanica hasnitrogen fixation capabilities via symbiosis and other species may as well.[6]
The species described byLinnaeus,Posidonia oceanica, is found in the Mediterranean; the rest are located around the southern coast of Australia. Some species are endemicseagrasses of Western Australia, all the Australian species are found in that region's diverse habitats.This arrangement was divided into two complexes: thePosidonia australis andPosidonia ostenfeldii groups.[11] Some species descriptions may only be regional characteristics, and may need further revision.[7][12]
In 2006 aclonal colony ofP. oceanica was discovered south of the island ofIbiza which measured 8 km across and is possibly up to 100,000 years old.[13]
^Cambridge, M.L. and Kuo, J. (1979) Two new species of seagrass from Australia,Posidonia sinuosa andPosidonia angustifolia (Posidoniaceae).Aquat. Bot.6, 307–328f. Keulen
^Kuo, J. and Cambridge, M.L. (1984) A taxonomic study of thePosidonia 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. 259:139f. 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. 6-73f. Keulen
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