The World's Biggest Plant Is A 180-Kilometer Meadow Of Self-Cloning Seagrass


Rachael Funnell

Social Editor and Staff Writer

clockJun 1 2022, 12:31 UTC
world's largest plant

This baby just keeps going. Image courtesy of UWA

An Australian seagrass clone has taken the title of "world’s largest plant", 4,500 years old and spanning a modest 180 kilometers (112 miles), say researchers from The University of Western Australia (UWA) and Flinders University. The discovery came about by accident after researchers were studying how many plants were contained within a seagrass meadow in Shark Bay – and were shocked that there was only one. The entire meadow was made up of just one big ol plant.


That plant is Poseidon’s ribbon weed, Posidonia australis, a fitting name for an award-winning seagrass. The clone spans at least 180 kilometers in the shallow waters of the World Heritage Area of Shark Bay, Western Australia, making it the largest known example of a clone in any environment on earth.

Tracking down Poseidon’s meadow began when researchers were asked to assess the genetic diversity of seagrass meadows in the area. They sampled seagrass shoots across Shark Bay – where marine plants tolerate extremes in temperature and salinity – and generated genetic fingerprints for the plants found using 18,000 markers.

How many plants did they find?

“The answer blew us away – there was just one!” said Jane Egeloe of UWA in a statement, who is the lead author on a paper about the plant published in Proceedings of the Royal Society B.


“That’s it, just one plant has expanded over 180km in Shark Bay, making it the largest known plant on earth. The existing 200km2 of ribbon weed meadows appear to have expanded from a single, colonising seedling.”

Beyond being a record-breaking beast of a seagrass clone, the enormous plant is puzzling scientists as its lack of a sex life (sorry, P. australis) means it would be expected to have limited genetic diversity, leaving it vulnerable to environmental change. However, the Poseidon meadow seems to be coping just fine with recent changes in Shark Bay.

“It experiences a huge range of average temperatures; from 17 to 30 °C,” said co-author Dr Martin Breed, an ecologist from Flinders University, in a statement. “Salinities from normal seawater to double that. And from darkness to extreme high light conditions. These conditions would typically be highly stressful for plants. Yet, it appears to keep on going.”


Its tolerance for extremes could be linked to the fact that it has twice as many chromosomes as its relatives, something it acquired through a process known as polyploidy.

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

“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.”


The researchers hope to continue their work on the Supersized Seagrass of Shark Bay to further uncover how this mega-plant has grown so voraciously despite its ever-changing environment.

  • plants,

  • cloning,

  • World records,

  • seagrass