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 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.
This is a list of species that are nominally contained by the genus:
- Posidonia angustifolia Cambridge and Kuo
- Posidonia australis Hook.f. South coast of Australia.
- Posidonia coriacea Cambridge and Kuo
- Posidonia denhartogii Kuo and Cambridge
- 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
- 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. Some species descriptions may only be regional characteristics, and may need further revision.
In 2006 a huge clonal colony of Posidonia oceanica, was discovered south of the island of Ibiza. At 8 km across and possibly up to 100,000 years of age, it may be one of the largest and oldest clonal colonies on Earth.
- Mike van Keulen. "The genus Posidonia König (nom. cons.) (Posidoniaceae).". Murdoch University. http://www.bsb.murdoch.edu.au/groups/seagrass/posidonia.html.
- 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" ([dead link]). Aquatic Botany 66 (1): pp. 41–56(16) Research article. DOI:10.1016/S0304-3770(99)00015-7. http://www.ingentaconnect.com/els/03043770/2000/00000066/00000001/art00015.
- Ibiza Spotlight (28 May 2006). "Ibiza's Monster Marine Plant". http://www.ibiza-spotlight.com/news/2006/monster_plant_280506_i.htm. Retrieved 2007-05-09.