Posidonia
Encyclopedia
Posidonia is a genus of flowering plant
s. It contains two to 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 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.
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.
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s. It contains two to nine species of marine plants ("seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
"), found in the seas of the Mediterranean and around the south coast of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
The APG system
APG system
The APG system of plant classification is the first, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in 1998 by the Angiosperm Phylogeny Group. It was superseded in 2003 by a revision, the APG II system, and then in 2009 by a further...
(1998) and APG II system
APG II system
The APG 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 Group. It was a revision of the first APG system, published in 1998, and was superseded in 2009...
(2003) accept this genus as constituting the sole genus in the family Posidoniaceae, which it places in the order Alismatales
Alismatales
Alismatales is an order of flowering plants including about 2500 species. Pleants assigned to this order are mostly tropical or aquatic.-Description:...
, in the clade monocots. The AP-Website concludes that the three families Cymodoceaceae, Posidoniaceae and Ruppiaceae
Ruppiaceae
Ruppia, also known as the ditch grasses, is the only genus in the family Ruppiaceae. Such a family has been recognized by relatively few taxonomists...
form a monophyletic group. Earlier systems classified this genus in the family Potamogetonaceae
Potamogetonaceae
The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. There are roughly 120 species spread across six genera in the Potamagetonaceae...
or in the family Posidoniaceae but belonging to order Zosterales.
Diversity
This is a list of species that are nominally contained by the genus:- Posidonia angustifolia Cambridge and Kuo
- Posidonia australisPosidonia australisPosidonia australis is a species of seagrass that occurs in the southern waters of Australia. It is sometimes referred to as Fibreball Weed. The marine plant forms large meadows that are considered to be of high importance to the environmental conservation of the region...
Hook.f. South coast of AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. - Posidonia coriaceaPosidonia coriaceaPosidonia 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 from 1 to 30 metres on white sands, in areas subject to intense...
Cambridge and Kuo - Posidonia denhartogii Kuo and Cambridge
- Posidonia kirkmanii Kuo and Cambridge
- Posidonia oceanicaPosidonia oceanicaPosidonia oceanica 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 floating and known in Italy as 'the olive of the sea'...
(L.) Delile - This plant is endemic to the Mediterranean SeaMediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, where it forms undersea meadowMeadowA meadow is a field vegetated primarily by grass and other non-woody plants . The term is from Old English mædwe. In agriculture a meadow is grassland which is not grazed by domestic livestock but rather allowed to grow unchecked in order to make hay...
s. - Posidonia ostenfeldiiPosidonia ostenfeldiiPosidonia 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 between 1 and 15 metres. The leaf blades are 6-12 mm...
den Hartog - Posidonia robertsoniaePosidonia robertsoniaePosidonia robertsoniae is one of the seagrasses of Western Australia, submerged flowering plants that occurs in the southern coastal waters.-Description:...
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
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 number of species...
, 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
Clonal colony
A clonal colony or genet is a group of genetically identical individuals that have grown in a given location, all originating vegetatively from a single ancestor. In plants, an individual in such a population is referred to as a ramet...
of Posidonia oceanica, was discovered south of the island of Ibiza
Ibiza
Ibiza or Eivissa is a Spanish island in the Mediterranean Sea 79 km off the coast of the city of Valencia in Spain. It is the third largest of the Balearic Islands, an autonomous community of Spain. With Formentera, it is one of the two Pine Islands or Pityuses. Its largest cities are 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.
External links
- Posidoniaceae in L. Watson and M. J. Dallwitz (1992 onwards) The families of flowering plants.
- Flora Europaea: Posidonia