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World’s largest plant observed off Australia

Researchers from the University of Western Australia recently announced that they have discovered the largest known plant on the planet in Shark Bay, located about 800km from the city of Perth. The study published in the journal Proceedings of the Royal Society B[1] reveals that this plant is none other than a Posidonia australis, seaweed common off the coast of Australia, and spans the equivalent of around 20,000 rugby stadiums. 4,500 years old, this ecological vestige has partly survived the extreme climatic events of recent years, but could unfortunately perish if the global temperature of the oceans continues to rise. This discovery reminds us of the importance of our ecosystems and the urgency of protecting them against the effects of climate change.

In shark bay, ecological heritage off the west coast of australiascientists recently made a startling discovery that once again reveals the unsuspected riches of the natural world. While on a quest to study the different plants present in an immense seagrass meadow in the bay, the genetic fingerprinting of the samples taken revealed that the entire seagrass bed was in fact consisting of a single specimen.

Growing like a lawn, the Posidonia australisWhere poseidon ribbon, usually expands at a rate of up to up to 35cm2 per year. Since then, covering no less than 200 km2about three times the size of the island of Manhattan, this algae, now considered to be the largest plant on the planet, would be about 4500 years old.

Located in a unique environment, very little disturbed by human activities and largely protected from ocean swells, this plant has long benefited from an environment favorable to its development:

“Yet subject to wide variations in temperature and salinity, as well as an extremely high level of luminosity, it seems particularly resilient in the face of these usually stressful conditions for most plants »[1]rejoiced Elizabeth Sinclair, one of the authors of the study announcing this discovery.

A particular genetics

The resilience of P. australis could potentially lie in his genetic fingerprint. Unlike many organisms that reproduce sexually, others use cloning techniques. Thus, a polyploid organism, this marine plant has twice the classic number of chromosomes.

Posidonia australis – Flickr
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Diploid organisms, like you and me, only inherit half of their parents’ genome, while this algae has all of it.. We therefore believe that having all the genes that helped him survive in his current environment, as well as those that could help him adapt to it, gave him an advantage in surviving the variable conditions of Shark Bay”[2]explains Dr. Sinclair.

Indeed, some areas have twice the salinity level that elsewhere in the bay, and in the whole of the latter, one can record temperature variations ranging from 15 to 30° C.

For Dr. Martin Breed, ecologist at Flinders University, this resilience is on the contrary a real enigma. In effect, Plants that do not have sex tend to have reduced genetic diversity, which they generally need to cope with climate change »[3], did he declare. He adds, however, that the plant developed very subtle genetic mutations depending on where it grew, which could therefore explain its extreme longevity.

Regarding the life expectancy of this seagrass, genetic studies on other similar species have revealed that these plants can indeed live between 2000 and 100,000 years ago. “Plants of the P. australis type have a versatile growth pattern that contributes to this long lifespan. They can grow into nutrient-rich patches, move to areas conducive to their growth, and thus move away from stressful regions.[4]explained Kathryn McMahon, a professor at Edith Cowan University and a seagrass specialist.

Unfortunately, climate change could threaten the future of this ecological treasure.

A fundamental ecosystem role

Sea grasses are plants that form real sea meadows in the shallow areas along the coasts. These are real allies in the fight against global warming and the collapse of biodiversity by providing essential ecosystem services[5]. Thereby :

  • They serve habitat and nursery, and represent a source of food for a wide variety of marine species;
  • protect the ribs by absorbing wave energy, or wave energy;
  • Participate in the oxygen production ; and especially
  • Constitute real carbon sink.

Indeed, although occupying only 0.2% of the seabedseagrass represents 10% of the carbon storage capacity of our oceansand can capture 15 times more carbon from the atmosphere and up to 35 times faster than rainforests[6].

Shark Bay – Flickr

However, the impact of climate change, urbanization, the development of human activities in coastal areas, and the degradation of water quality due to anthropogenic pollution accelerate the decline of seagrass bedswith recorded losses similar to those of coral reefs and rainforests.

In Shark Bay, the extreme marine heat wave that affected Australia from 2010 to 2011, for example, damaged approximately 36% of the P. australis peerage:

“These damages are likely to have released into the atmosphere much of the carbon that was locked up there. In addition, the bay is home to exceptional megafauna such as dugongs, turtles, dolphins and thousands of species of fish. Once the seagrass disappears, all of the biodiversity of a higher trophic level is impacted, and therefore threatened » recalls Jane Edgeloe, doctoral student and lead author of the study.

Whereas 159 signatory countries of the Paris agreement have seagrass beds on their coasts, the development of ambitious policies for the protection and restoration of these marine ecosystems seems fundamental to combating the effects of global warming.


[1] Turnbull, T.,” World’s biggest plant discovered off Australian coast” in BBC News, 1 June 2022, available at:

[2] Ashworth, J., “The world’s largest plant is an Australian seagrass clone” in Natural History Museum News, 1 June 2022, available at:

[3] Readfearn, G. “Scientists discover biggest plant on Earth off Western Australian Coast” in The Guardian, 1 June 2022, available at: ?CMP=fb_gu&utm_medium=Social&utm_source=Facebook#Echobox=1654063547

[4] Ibid., =Social&utm_source=Facebook#Echobox=1654063547

[5] WFF, Planting Hope: Seagrass, available at:; The Wildlife Trusts, Natural solutions to the climate crisis – Super seagrass, available at:

[6] A P, Seagrass – secret weapon in the fight against global heating, November 1, 2019, available at:

[1] Edgeloe, A. Extensive polyploid clonality was a successful strategy for seagrass to expand into a newly submerged environment, Proceedings of the Royal Society B, June 1, 2022, available at:



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