Researchers find world’s largest plant in Australia after mistaking it for giant underwater meadow

A single seed from 4,500 years ago spread to form the plant that has developed resilience to recover from an extreme climate event

Scientists have discovered the world’s largest plant growing underwater after initially mistaking it for a giant underwater meadow.

The plant, discovered at Shark Bay, a World Heritage site located off the Western Australia coast, is believed to span as much as 200sq km (77sq miles). This surface area is slightly larger than the city of Glasgow, more than times the size of Manhattan Island or roughly 20,000 rugby fields.

Experts believe the plant spread from a single seed about 4,500 years ago and has been growing ever since.

The study, which was published on Wednesday in the Proceedings of the Royal Society B journal, is piquing the curiosity of scientists across the world.

Researchers say that the plant is a single clone of a 180km-long Posidonia australis seagrass, making it the largest known example of a clone in any environment on Earth.

The discovery was made by accident, scientists say, after stumbling across the plant while carrying out genetic testing. What was initially believed to be a giant seagrass meadow actually turned out to be a single massive P australis polyploid clone.

Polyploidy is a feature usually common in plants that allows them to have more than one pair of chromosomes.

The new polyploid clone is believed to have formed in shallow waters after the inundation of the Shark Bay area less than 8,500 years ago, which researchers said is likely to have subsequently expanded via vegetative growth into newly submerged habitats.

“We were quite surprised when we had a good look at the data and it seemed to indicate that everything belonged to the one plant,” evolutionary biologist and study co-author Elizabeth Sinclair, from the University of Western Australia, told ABC Australia.

Apart from the unusual size of the plant, researchers said its ability to sustain itself for thousands of years suggests it has developed resilience to recover from an extreme climate event via vegetative growth.

“Exactly how the polyploid clone varies its response to local environmental conditions is unknown and the subject of further research, but its relative abundance suggests that it has evolved a resilience to variable and often extreme conditions that enable it to persist now and into the future,” the researchers said.