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".

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.

“The result blew us away”

"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 seagrass shoots from numerous spots in the bay and "fingerprinted" them from 18,000 genetic markers, explained lead author Jane Edgeloe.

Then came the surprise: all the samples were genetically identical

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the plant is therefore a single coherent organism.

"The result just blew our minds

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there was only one plant, stretching 180 kilometers." The seagrass meadow likely arose from a "single, colonizing seedling" that kept spreading, Edgeloe said.

Given the enormous size, experts estimate that the plant must have grown for around 4,500 years.

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," the study says.

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".