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''Posidonia australis'', also known as fibre-ball weed or ribbon weed, is a species of
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 orde ...
that occurs in the southern waters of Australia. It forms large meadows important to environmental conservation. Balls of decomposing detritus from the foliage are found along nearby shore-lines. In 2022, a single stand in
Shark Bay Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
was reported by scientists to be the largest plant in the world.


Description

''Posidonia australis'' is a flowering plant occurring in dense meadows, or along channels, in white sand. It is found at depths from . Subsurface
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
s and roots provide stability in the sands it occupies. Erect rhizomes and leaves reduce the accumulation of
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
. The leaves are ribbon-like and wide. They are bright green, perhaps becoming browned with age. The terminus of the leaf is rounded or absent through damage. They are arranged in groups with older leaves on the outside, longer and differing in form from the younger leaves they surround. The species is
monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...
. The flowers appear on small spikes on leafless stems, two bracts on each spike. The plant pollinates by
hydrophily Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams. Hydrophilous species fall into two categories: (i) Those that distribute their pollen to the surface of ...
, by dispersing in the water. ''Posidonia australis'' reproduction usually occurs through sexual or asexual methods but, under extreme conditions, by pseudovivipary. A 2013 study showed that ''P. australis'' can sequester carbon 35 times more efficiently than
rainforests Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainforest ...
. In 2022, a study by the School of Biological Sciences and Oceans Institute at The University of Western Australia showed that a single plant of this species can grow
vegetatively Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...
by using
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
s to cover an extensive area, similar to
buffalo grass Buffalo grass may refer to * Buffalo grass, sweet vernal grass or vanilla grass ('' Anthoxanthum odoratum'') * Buffalo grass ('' Bouteloua dactyloides'') * Buffalo grass ('' Brachiaria mutica'') * Buffalo grass or sweet grass (''Hierochloe odorata' ...
. This particular specimen has double the number of chromosomes of other studied populations (40 chromosomes instead of the usual 20).


Distribution

This species is found in waters around the southern coast of Australia. In
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
is occurs in the
Shark Bay Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
region, around islands of the
Houtman Abrolhos The Houtman Abrolhos (often called the Abrolhos Islands) is a chain of 122 islands and associated coral reefs, in the Indian Ocean off the west coast of Australia, about west of Geraldton, Western Australia. It is the southernmost true coral ...
, and southward along the coast of the
Swan Coastal Plain The Swan Coastal Plain in Western Australia is the geographic feature which contains the Swan River as it travels west to the Indian Ocean. The coastal plain continues well beyond the boundaries of the Swan River and its tributaries, as a geol ...
. The species is recorded at the edge of the
Esperance Plains Esperance Plains, also known as Eyre Botanical District, is a biogeographic region in southern Western Australia on the south coast between the Avon Wheatbelt and Hampton bioregions, and bordered to the north by the Mallee region. It is a pl ...
, the
Archipelago of the Recherche The Archipelago of the Recherche, known locally as the Bay of Isles, is a group of 105 islands, and over 1200 "obstacles to shipping", off the south coast of Western Australia. The islands stretch from east to west and to off-shore encomp ...
, at the southern coast of the southwest region. The range extends to the east to coastal areas of New South Wales, South Australia, Tasmania, and Victoria. A sign of a nearby occurrence of ''
Posidonia ''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 ...
'' is the presence of masses of decomposing leaves on beaches, forming fibrous balls.


Largest known organism

A research article in the Proceedings of the Royal Society reported in June 2022 that genetic testing had revealed that samples of ''Posidonia australis'' taken from a meadow in
Shark Bay Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
up to apart were all from a single clone of the same plant. The plant covers an area of
seafloor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...
of around . This would make it the largest known organism in the world by area, exceeding the size of a colony of the ''
Armillaria ostoyae ''Armillaria ostoyae'' (synonym ''Armillaria solidipes'') is a species of fungus (mushroom), pathogenic to trees, in the family Physalacriaceae. In the western United States, it is the most common variant of the group of species under the nam ...
'' fungus in
Malheur National Forest The Malheur National Forest is a United States National Forest, National Forest in the U.S. state of Oregon. It contains more than in the Blue Mountains (Pacific Northwest), Blue Mountains of eastern Oregon. The forest consists of Great Basin ...
,
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
that extends , as well as a stand of quaking aspen trees in
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
that extends over more than . The plant is estimated to have taken at least 4,500 years to grow to this size by using
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
s to colonise new parts of the seafloor, assuming a rhizome growth rate of around a year. This age puts it among the oldest known clonal plants too.


Taxonomy

This species is a member of the family
Posidoniaceae ''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 ...
, one of eight occurring in Australia. The ninth member, ''
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 ...
'', is found in the Mediterranean sea. The genus name for this species, ''Posidonia'', is given for the god of the seas
Poseidon Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...
, and ''australis'' refers to the southern distribution. The species was first described by
Joseph Hooker Joseph Hooker (November 13, 1814 – October 31, 1879) was an American Civil War general for the Union, chiefly remembered for his decisive defeat by Confederate General Robert E. Lee at the Battle of Chancellorsville in 1863. Hooker had serv ...
in ''
Flora Tasmaniae The ''Flora Tasmaniae'' is a description of the plants discovered in Tasmania during the Ross expedition written by Joseph Dalton Hooker and published by Reeve Brothers in London between 1855 and 1860. Hooker sailed on HMS ''Erebus'' as assistant ...
''.
Common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...
s for the plant include fibre-ball weed and ribbon weed.


Conservation status

IUCN lists this species as "near threatened", while the meadows in New South Wales have been listed by the
Commonwealth of Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
as an endangered ecological community since 2015.


Bioactivity

A recent ''
in silico In biology and other experimental sciences, an ''in silico'' experiment is one performed on computer or via computer simulation. The phrase is pseudo-Latin for 'in silicon' (correct la, in silicio), referring to silicon in computer chips. It ...
'' study showed that the leaf proteins of ''Posidonia australis'' could be a good source of antioxidant peptides when consumed by humans. The
virtual screening Virtual screening (VS) is a computational technique used in drug discovery to search libraries of small molecules in order to identify those structures which are most likely to bind to a drug target, typically a protein receptor or enzyme. Virtua ...
study reported that such peptides could participate in the scavenging of
free radicals In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spont ...
. They could also potentially inhibit the activities of
myeloperoxidase Myeloperoxidase (MPO) is a peroxidase enzyme that in humans is encoded by the ''MPO'' gene on chromosome 17. MPO is most abundantly expressed in neutrophil granulocytes (a subtype of white blood cells), and produces hypohalous acids to carry ou ...
,
xanthine oxidase Xanthine oxidase (XO, sometimes XAO) is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species. These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthin ...
, and Kelch-like ECH-associated protein, thus reducing cellular production of
reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...
.


References


External links


''Posidonia australis'' occurrence data
from
Australasian Virtual Herbarium The ''Australasian Virtual Herbarium'' (AVH) is an online resource that allows access to plant specimen data held by various Australian and New Zealand herbaria. It is part of the Atlas of Living Australia (ALA), and was formed by the amalgamat ...
* * {{Taxonbar, from=Q3399633 australis Flora of New South Wales Flora of South Australia Flora of Tasmania Flora of Victoria (Australia) Angiosperms of Western Australia Monocots of Australia Largest organisms