The ribbon weed meadow in the Australia’s Shark Bay has been revealed to be made up of a single plant, making it the world’s biggest plant. 

The world’s largest living plant has been identified in the shallow waters off the coast of Western Australia, after scientists conducted genetic testing at the seagrass meadow. 

The Posidonia australis, or more commonly as ribbon weed or fibre-ball weed, is located in the UNESCO World Heritage Site of Shark Bay. The seagrass meadow stretches 180 kilometres (112 miles), equivalent to the distance between San Diego and Los Angeles.

To better understand what makes the meadow so large and to discover how many different plants are growing there, Elizabeth Sinclair, a senior research fellow at the School of Biological Sciences and Oceans Institute at The University of Western Australia, and her colleagues began taking genetic samples from 10 locations taken in 2012 and 2019. What they found, however, is that the meadow is not made up of multiple species but a single plant. 

“The answer definitely surprised us – just ONE! That’s it, just one plant has expanded over 180 km in Shark Bay, making it the largest known plant on Earth,” Sinlar wrote in an email to CNN. The recent discovery therefore overtakes the stand of quaking Aspen trees in Utah – which covers 43 hectares – as the world’s largest plant. 

The existing 200 sq km of ribbon weed meadows appear to have expanded from a single, colonising seedling, according to the research team. It clones itself using rhizomes to create genetically identical offshoots, a process that is rare in the animal kingdom but a little more so with plants, fungi and bacteria. 

Ribbon weed rhizomes can grow up to 35cm a year. Based on this, the researchers estimate that the plant took at least 4,500 years to grow to the size it is today. It now provides a widespread habitat for a stunning range of marine species including turtles, dolphins, dugongs, crabs and fish.

The team published their findings in a paper in the journal Proceedings of Royal Society B, and said they also measured the environmental conditions such as water temperature and salinity, which could be key in understanding the ribbon weed’s adaptability amid increased salinity and temperature rise. 

The ribbon weed is found surviving and even thriving in waters with double the salinity compared to other areas in Shark Bay. It also seems relatively unaffected by fluctuating temperatures; water has been recorded to be as low as 15C and as high as 30C.

The study also suggests that its cloning process and how each offshoot carries all the chromosomes from its two parents are related to the plant’s adaptability, even though plants that don’t have sex tend tend to have reduced genetic diversity, which they normally need when dealing with environmental change, according to Dr Martin Breed, fellow researcher and an ecologist at Flinders University

Though it’s too early to tell, the discovery could lead to better understanding of how other marine plant species could adapt as ocean conditions continue to change and fluctuate, including higher acidity and temperatures. Seagrass is also one of the most important carbon capturing and storing (carbon sequestration) habitats we have; further development or restoration projects could potentially help ease the impacts of climate change as well.

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