This is the world's largest living plant and it's at least 4,500 years old

Scientists discovered the world's largest plant, a seagrass that covers more than 200 square kilometers (77 square miles), just over three times the size of Manhattan. The single seagrass Posidonia australis, thought to be more than 4,500 years old, lives in the shallow waters of Western Australia's Shark Bay, a World Heritage Site. From the University of Western Australia:

Evolutionary biologist Dr Elizabeth Sinclair, from UWA's School of Biological Sciences and the UWA Oceans Institute, is a senior author of the study and 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 said. "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."

image: Shark Bay, Angela Rossen/UWA