The researchers estimated the plant to be 4,500 years old.
Researchers have found an extensive seagrass meadow in Shark Bay, Western Australia, about 20,000 football fields in size.
Further investigation revealed that it was a single plant up to 180 kilometers wide.
The plant had spread over such a wide area because the coastal waters of the Shark Bay area are shallow and the plant received plenty of sun for this reason.
The researchers estimated the plant to be 4,500 years old.
The seagrass Posidonia australis is a common plant off the coast of Australia.