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World’s largest plant discovered in Australia. It stretches 112 miles and is at least 4500 years old.

'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.'

World’s largest plant discovered in Australia. It stretches 112 miles and is at least 4500 years old.
Cover Image Source: University of Western Australia

Editor's Note: This article was originally published on June 10, 2022. It has since been updated.

The world's biggest plant has been discovered in the shallow waters off the coast of Western Australia, according to researchers from the University of Western Australia and Flinders University. The sprawling seagrass, a marine flowering plant known as Posidonia australis, reportedly stretches for more than 112 miles (180 kilometers) and is at least 4,500 years old. Speaking to CNN, Elizabeth Sinclair—a senior research fellow at the School of Biological Sciences and Oceans Institute at the University of Western Australia—revealed that the plant was discovered in the shallow, sun-drenched waters of Shark Bay, a wilderness area protected as a World Heritage Site.



 

 

In a study published in the journal Proceedings Of The Royal Society B, the team explained that the plant is so large—about as big as the distance between San Diego and Los Angeles—because it clones itself, creating genetically identical offshoots. Although this way of reproducing is rare in the animal kingdom, it reportedly occurs in certain environmental conditions and more often among some plants, fungi and bacteria. "We often get asked how many different plants are growing in a seagrass meadow. Here we used genetic tools to answer it," said Sinclair, the author of the study.



 

 

"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," she added. According to BBC, the team stumbled upon the discovery by accident. They set out to understand the genetic diversity of sprawling seagrass—which is also known as ribbon weed—commonly found along parts of Australia's coast. Sinclair and her colleagues took samples from 10 locations across the bay and examined 18,000 genetic markers to create a "fingerprint" from each sample. They also measured the environmental conditions such as depth, water temperature and salinity.



 

 

"We have been studying cool water seagrasses in southern Australia for a while, to understand how much genetic diversity is in them and how connected the meadows are," Sinclair said. Although they aimed to discover how many plants made up the meadow, sequencing DNA from the seagrass samples revealed that it was a single plant. "The plant has been able to continue growing through vegetative growth–extending its rhizomes (rootstalk) outwards–the way a buffalo grass would in your back garden, extending runners outwards. The only difference is that the seagrass rhizomes are under a sandy seafloor, so you don’t see them, just the shoots within the water column," she explained.



 

 

The plant is also remarkable for its hardiness, Sinclair said, as it appears to have grown in locations across the bay with wildly variable conditions. "It appears to be really resilient, experiencing a wide range of temperatures and salinities plus extreme high light conditions, which together would typically be highly stressful for most plants," she said. Sinclair explained in a press release what makes this seagrass plant unique from other large seagrass clones (aside from its enormous size) is that it has twice as many chromosomes as its oceanic relatives, meaning it is a polyploid.



 

 

"Whole-genome duplication through polyploidy–doubling the number of chromosomes–occurs when diploid 'parent' plants hybridize. The new seedling contains 100 percent of the genome from each parent, rather than sharing the usual 50 percent," she said. "Polyploid plants often reside in places with extreme environmental conditions, are often sterile, but can continue to grow if left undisturbed, and this giant seagrass has done just that."

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