A giant carpet of seagrass off the coast of Western Australia has been revealed to be a single organism by research. Probably the largest plant in the world has grown over thousands of years.

Researchers in Australia have discovered what is believed to be the largest plant in the world: the seagrass carpet off the west coast of the country stretches over 180 kilometers and is estimated to be at least 4500 years old.

The plant of superlatives is the seaweed species Posidonia australis, as researchers from the University of Western Australia and Flinders University in Adelaide report in the journal “Proceedings of the Royal Society B”.

A chance find

The botanical wonder was discovered in Shark Bay, about 800 kilometers north of Perth, which has been a UNESCO World Heritage Site since 1991. The scientists only made the find by accident: Originally, they wanted to find out how genetically diverse a seagrass meadow is and took samples for this purpose.

“We’re often asked how many different plants grow in seagrass beds, and this time we used genetic tools to answer that,” said evolutionary biologist Elizabeth Sinclair. The team collected seaweed shoots from numerous spots in the bay and created a “fingerprint” from 18,000 genetic markers, explained lead author Jane Edgeloe.

Then the surprise: All samples were genetically identical – the plant is therefore a single coherent organism. “The result just blew us away – there was only one plant that stretches over 180 kilometers.” Edgeloe said the seagrass meadow likely grew out of a “single, colonizing seedling” that kept spreading. Given the enormous size, experts estimate that the plant must have grown for around 4,500 years.

Ideal growing conditions

The shallow environment of Shark Bay with its sandy sediments is ideal for the clonal growth of seagrass beds. How the plant managed to survive for so long and still thrive so well is a mystery. Further studies should now clarify why the clone copes so well with changing environmental conditions. What is certain is that “he has developed a resilience to variable and often extreme conditions that enables him to survive now and in the future,” says the study.

Just a few years ago, researchers in North America discovered a huge network of 47,000 aspen trees with identical genetic makeup, connected underground by roots. This so-called pando has probably also existed for thousands of years. This “forest from a tree” weighs 5.9 million kilograms and grows on 43 hectares, wrote the team led by Paul Rogers from Utah State University in 2018 in the journal “PLOS One”. “Pando” is Latin and means “I spread”.