''Posidonia'' is a genus of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s. It contains nine species of marine plants ("

seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...

"), found in the seas of the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

and around the south coast of Australia. The

APG system The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular-based, system of plant taxonomy. Published in 1998 by the Angiosperm Phylogeny Group, it was replaced by the improved A ...

(1998) and

APG II system The APG II system (Angiosperm Phylogeny Group II system) of plant classification is the second, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in April 2003 by the Angiosperm Phylogeny Gr ...

(2003) accept this genus as constituting the sole genus in the family Posidoniaceae, which it places in the order

Alismatales The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly Tropical vegetation, tropical or Aquatic plant, aquatic. Some grow in fresh water, some in marine habitats. ...

, in the clade

monocots Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...

. The AP-Website concludes that the three families

Cymodoceaceae Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass family", which includes only marine species. The 2016 APG IV does recognize Cymodoceaceae and places it in the order Alismatales, in the clade monocots. The fam ...

, Posidoniaceae and

Ruppiaceae ''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with eight known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich ...

form a monophyletic group. Earlier systems classified this genus in the family

Potamogetonaceae The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. The roughly 110 known species are divided over six genera. The largest genus in the family by far is ''Potamogeton'', w ...

or in the family Posidoniaceae but belonging to order Zosterales. ''Posidonia oceanica'' has

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

capabilities via symbiosis and other species may as well.

Species

This is a list of species that are contained by the genus: *'' Posidonia angustifolia'' Cambridge and Kuo *''

Posidonia australis ''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 ...

Hook.f. Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For twenty years he served as director of ...

South coast of Australia. *''

Posidonia coriacea ''Posidonia coriacea'' is a species of seagrass that occurs in the southern waters of Australia. Description A species of ''Posidonia''. A perennial rhizomatous herb that appears as stands in marine habitat. This species is found at depths fro ...

'' Cambridge and Kuo *'' Posidonia denhartogii'' Kuo and Cambridge *''

Posidonia kirkmanii ''Posidonia'' is a genus of flowering plants. It contains nine species of marine plants ("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 ge ...

'' Kuo and Cambridge *''

Posidonia oceanica ''Posidonia oceanica'', commonly known as Neptune grass or Mediterranean tapeweed, is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free f ...

'' ( L.)

Delile Alire Raffeneau Delile (23 January 1778, in Versailles – 5 July 1850, in Montpellier) was a French botanist. Biography Delile studied botany with Jean Lemonnier, and was in the Paris medical school in 1796. Egypt Delile participated in Napole ...

– This plant is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

, where it forms undersea

meadow A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non- woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or arti ...

s. *''

Posidonia ostenfeldii ''Posidonia ostenfeldii'' is a species of seagrass that occurs in the southern waters of Australia. Description A species of ''Posidonia''. A perennial rhizomatous herb that appears as clumps on sand in marine habitat. It is found at depths be ...

'' den Hartog *'' Posidonia robertsoniae'' Kuo and Cambridge *''

Posidonia sinuosa ''Posidonia'' is a genus of flowering plants. It contains nine species of marine plants ("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 gen ...

'' Cambridge and Kuo The species described by

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

, ''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 The Seagrasses of Western Australia are submerged flowering plants found along the coast, around islands, and in Estuaries of Western Australia. The region contains some of the largest seagrass meadows in the world, and is the most diverse in the nu ...

, 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 clonal colony of ''P. oceanica'' was discovered south of the island of Ibiza which measured 8 km across and possibly up to 100,000 years old.

Taxonomy

References

External links

*
Posidoniaceae
in L. Watson and M. J. Dallwitz (1992 onwards
The families of flowering plants

Flora Europaea: ''Posidonia''
{{Taxonbar, from=Q877147 Alismatales genera Taxa named by Charles Konig