The ancient plant appears to have expanded from a single, seedling (Picture: Rachel Austin)

Researchers have located the largest plant in the world that’s roughly as long as the distance between London and Bath.

Th plant is an ancient and incredibly resilient seagrass stretching across 180km and is estimated to be at least 4,500 years old.

Scientists discovered the plant in the shallow, sun-drenched waters of the Shark Bay in Western Australia, a world heritage site.

The single plant consisting of 200 square kms of ribbon weed meadows is actually a ‘clone’ of the seagrass Posidonia australis that appears to have expanded from a single, colonising seedling.

The discovery was made by researchers from the University of Western Australia (UWA) and Flinders University who published their finding in Proceedings of the Royal Society B

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. 

Scientists discovered the plant in the shallow, sun-drenched waters of the Shark Bay in Western Australia (Picture:  Angela Rossen)

‘We often get asked how many different plants are growing in seagrass meadows and this time we used genetic tools to answer it,’ said Dr Elizabeth Sinclair, an evolutionary biologist from UWA and senior author of the study.

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!’ said Edgeloe. ‘That’s it, just one plant has expanded over 180km in Shark Bay, making it the largest known plant on earth,’

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

‘Whole genome duplication through polyploidy – doubling the number of chromosomes – occurs when diploid “parent” plants hybridise. The new seedling contains 100 per cent of the genome from each parent, rather than sharing the usual 50 per cent,’ said Dr Sinclair. 

‘Polyploid plants often reside in places with extreme environmental conditions, are often sterile, but can continue to grow if left undisturbed, and this giant seagrass has done just that,’

Even without without successful flowering and seed production, the plant appears to be a fighter, braving a wide range of temperatures and salinities plus extreme high light conditions, which together would typically be highly stressful for most plants.

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.


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