Largest known plant on earth discovered at Shark Bay, and it's 4,500 years old.Researchers from The University of Western Australia and Flinders University have located what is believed to be the largest plant in the world – an ancient and incredibly resilient seagrass stretching across 180km that is estimated to be at least 4,500 years old.The discovery of the single plant or ‘clone’ of the seagrass Posidonia australis in the shallow, sun-drenched waters of the World Heritage Area of Shark Bay in WA…