Scientists in Australia have discovered what is believed to be the largest plant in the world.

Researchers from the University of Western Australia and Flinders University have located an ancient and incredibly resilient seagrass stretching across 180km that is estimated to be at least 4,500 years old in Western Australia’s World Heritage Area, Shark Bay.

The discovery of the single plant or ‘clone’ of the seagrass Posidonia australis in the shallow, sun-drenched waters is detailed in a new study published in Proceedings of the Royal Society B. Evolutionary biologist.

Dr Elizabeth Sinclair, from UWA’s School of Biological Sciences and the UWA Oceans Institute, said the project began when researchers wanted to understand how genetically diverse the seagrass meadows in Shark Bay were, and which plants should be collected for seagrass restoration.

“We often get asked how many different plants are growing in seagrass meadows and this time we used genetic tools to answer it,” Dr Sinclair said.

UWA student researcher Jane Edgeloe, lead author of the study, said the team sampled seagrass shoots from across Shark Bay’s variable environments and generated a ‘fingerprint’ using 18,000 genetic markers.

“The answer blew us away – there was just one!” Ms Edgeloe exclaimed. “That’s it, just one plant has expanded over 180km in Shark Bay, making it the largest known plant on earth. “The existing 200km2 of ribbon weed meadows appear to have expanded from a single, colonising seedling.”

Dr. Sinclair said what makes this seagrass plant unique from other large seagrass clones, other than its enormous size, is that it has twice as many chromosomes as its oceanic relatives, meaning it is a polyploid.

The researchers have now set up a series of experiments in Shark Bay to understand how this plant survives and thrives under such variable conditions.