4,500-year-old plant found off Australian coast is world's largest: study

Australian scientists have discovered what they say is the largest living plant on Earth: ancient seagrass dating back thousands of years off the country's west coast.

Found in the ocean in Shark Bay, a UNESCO World Heritage Site located approximately 800 kilometres north of the city Perth in Western Australia, the massive seagrass is at least 4,500 years old, scientists say, and is 200 square kilometres in size.

The findings are included in a study, developed by researchers at the University of Western Australia and Flinders University in South Australia, published recently in the journal Proceedings of the Royal Society B.

"It's a largely pristine environment and it's largely remained undisturbed at all from major human development," Elizabeth Sinclair, an evolutionary biologist from the University of Western Australia and the study's senior author, told CTV National News.

Adding to the intrigue is the discovery that the plant, whose species name is Posidonia australis, came from one seed that has cloned itself for thousands of years.

Using 18,000 genetic markers, the researchers sampled seagrass shoots from across Shark Bay in an effort to understand how genetically diverse the plants were.

"The answer blew us away — there was just one,” Jane Edgeloe, a University of Western Australia student researcher and lead author of the study, said in a statement.

"That's it, just one plant has expanded over 180 kilometres in Shark Bay, making it the largest known plant on Earth."

The plant has also proven resilient to wide temperature fluctuations, as well as high salinity and light conditions, the researchers say.

They say they are now creating experiments to understand how the plant survives under these different conditions.

This resiliency is also giving scientists hope in the fight against climate change.

"So they are powerhouses for sort of cleaning and filtering the water ... and so it's extremely hopeful to think that life, in this case it's seagrass, has found a way to persist," Mary O'Connor, a zoology professor at the University of British Columbia, said.

Although Australia is now laying claim to the new record, others are as well.

"We don't know what’s going on down under but up at our elevation we know Colorado's gorgeous Aspen groves (and Utah's as well) is a sight to behold and are the world's largest plant," Colorado Gov. Jared Polis said on Twitter.

And who knows. Canada, which has the longest coastline in the world, could be in the running.

"Yeah, I would throw Canada's ticket in the ring for sure for this competition," O'Connor said.

"Challenge accepted. We'll find out."

We don’t know what’s going on down under but up at our elevation we know Colorado’s gorgeous Aspen groves (and Utah’s as well) is a sight to behold and are the world’s largest plant. pic.twitter.com/W5tsaylhnx

— Governor Jared Polis (@GovofCO) June 2, 2022