Researchers discover world’s largest plant measuring 180 km’s in length

Biologists from the University of Western Australia and Flinders University have identified the worlds largest known plant, an ancient seagrass thought to be 4,500 years old.

The discovery, now published in the Proceedings of the Royal Society B reveals identifies 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 Western Australia.

Posidonia australis, also known as fibre-ball weed or ribbon weed, is a species of seagrass that grows in dense meadows, or along channels in white sand.


The discovery was made during a project to understand the genetic diversity of grass meadows in Shark Bay, and which plants should be collected for seagrass restoration.

Covering an area of 200km2, the seagrass meadow appears to have expanded from a single colonising seedling, making it the largest known organism in the world, exceeding the size of a colony of the Armillaria ostoyae fungus in Malheur National Forest, Oregon that extends 9.1km2, as well as a stand of quaking aspen trees in Utah that extends more than 0.4km2.

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.

Dr Sinclair said what makes this seagrass plant unique from other large seagrass clones, other than its enormous size, 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,” Dr Sinclair said.

“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 successful flowering and seed production, it appears to be really resilient, experiencing 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.

The University of Western Australia

Header Image Credit : Mike Workman – Shutterstock

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