The world’s largest plant has been found hiding in plain sight in Western Australia and is at least as old as Egypt’s great pyramids.
The aquatic ribbon weed, which covers about 200 square kilometres of picturesque Shark Bay, about 400km north of Geraldton, was long believed to be a collection of genetically varied individuals.
But tests have revealed a startling truth – genetically speaking it is all one entity that began life about 4500 years ago when the ancient Egyptians were busy building their famed pyramids at Giza.
There are older seagrasses and terrestrial plants elsewhere in the world, but none are believed to be as large as the Shark Bay wonder.
Flinders University ecologist Dr Martin Breed co-authored a recently published study on the ribbon weed and has a handy analogy to explain its extraordinary longevity.
“It’s like someone’s lawn. It grows through rhizomes, these underground suckers, and then it pops up and green shoots appear,” he said.
“What we’ve observed in Shark Bay is essentially an extremely large lawn that has expanded and grown across a very large area.
“There are some parts of the lawn that have died but there’s lots of parts that are still alive.”
The study’s senior author, University of Western Australia evolutionary biologist Dr Elizabeth Sinclair, said the ribbon weed is a polyploid, meaning it has twice as many chromosomes as its oceanic relatives.
And that could explain its durability.
“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,” she said.
“Even without successful flowering and seed production, 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.”
University of Western Australia student researcher Jane Edgeloe said researchers sampled seagrass shoots from across Shark Bay’s variable environments and generated a “fingerprint” using 18,000 genetic markers.
She said they were blown away to realise the huge expanse was just one plant – the largest known to exist on earth.
“The existing 200 square kilometres of ribbon weed meadows appear to have expanded from a single, colonising seedling,” she said.
Researchers have now set up a series of experiments in Shark Bay to understand how the plant survives and thrives under such variable conditions.
Dr Breed said the plant, which provides vital habitat for dolphins, dugongs and fish, took a big hit in 2010/11 when a marine heatwave struck, pushing water temperatures 4C above average.
But it has bounced back, and that is cause for optimism in the face of increasing stresses caused by climate change.
“It seems to have a way to hunker down and have the genetic toolkit to survive, no matter what conditions have been thrown at it so far,” he said.
The research has been published in the journal Proceedings of the Royal Society B.
