Researchers have revealed that a plant about 4,500 years old and 180 kilometers across is living in the water in Western Australia.
Genetic testing revealed the presence of giant seagrass beds in the shallow waters of Shark Bay, near Carnarvon. Seagrass is a flowering plant that can grow well in shallow marine environments.
All seagrasses are one-seeded plants that have roots, rhizomes, leaves, flowers and fruit as well as vascular plants that grow on land. So very different from seaweed.
According to the researchers, who published their findings in Proceedings of the Royal Society B, this makes it the largest plant known to exist on Earth.
"Certainly based on land area, to the best of our knowledge, this is the largest plant in the world," said evolutionary biologist and study co-author Elizabeth Sinclair of the University of Western Australia.
"We were quite surprised when we took a good look at the data and it seemed to indicate that they all belonged to one source."
The researchers initially set out to study how genetically diverse the seagrass beds are. But they had a hunch that there was something a little odd about the seagrass in the area, according to study co-author, ecologist and ecosystem health researcher Martin Breed of Flinders University.
"We were a little suspicious because the plants around there weren't behaving like regular seagrasses. They weren't flowering much, not much seed, so these signs of reproductive activity were a bit mundane," said Dr Breed.
But when they sampled 10 prairies across the Shark Bay area, they never expected nine of them to produce a genetic match.
"We went there without any prior idea about finding the largest plant on Earth," said Dr Breed.
Instead, they plan to use their research to inform which crops to use for grassland restoration, to help them withstand threats such as bleaching.
"Our PhD student Jane Edgleloe did the DNA work and we quickly realized that it was much more complicated than we expected. It surprised us," said Dr Breed.
Dr Sinclair said these plants had spread over about 200 square kilometers and that plants with the same genetic fingerprint were spread out for about 180 km.
"The reason why this plant can continue to grow is because most of its habitat is undisturbed. It is a beautiful world heritage site," he said.