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Ometecuhtli writes:

https://www.abc.net.au/news/science/2022-06-01/worlds-largest-plant-seagrass-meadow-shark-bay-giant-clone/101112726 [abc.net.au]

"... But researchers have today revealed there's a plant about 4,500 years old and measuring 180 kilometres across living right under our noses in Western Australia.

Genetic testing has revealed that what was once thought to be part of a giant seagrass meadow in the shallow waters of Shark Bay, near Carnarvon, was actually a single massive clone of Posidonia australis seagrass...

... "We were a bit suspicious because the plants around there don't act like normal seagrass," Dr Breed said.

"They don't flower as much, don't seed as much, so these signs of reproductive activity were a little bit unremarkable."

But when they took samples from 10 meadows throughout the Shark Bay area, they never expected nine of them to return a genetic match.

Instead, they were planning to use their research to inform which plants to use for restoration of the meadows, to help with their resilience against threats like bleaching...

.. Being a clone probably helps to explain why this single plant has been so successful...

...Polyploidy in this case has occurred because at some stage, a Posidonia plant has hybridised with another related species.

The disadvantage of this is that it is no longer able to reproduce sexually, so doesn't get any genetic variation across generations that might allow it to adapt to changing conditions over time.

But the plus side is it possesses double the amount of genetic variability to begin with.

"What that does is double the amount of genetic diversity you have in that plant and probably broadens its capacity to deal with the challenges that come from its environment," Dr Sinclair said.

While polyploidy can be a disadvantage, the conditions in Shark Bay are extremely variable and having double the chromosomes appears to be paying off for the Posidonia, according to Dr Breed.

"It can be 17 degrees in the water one day and 30 degrees the next and the salinity [varies widely]. The seagrass is able to hold the fort even when you've got massively fluctuating conditions," Dr Breed said.

"There was a big heatwave in 2010 -2011 — about a third of seagrasses were knocked off. But [it] bounced back very well."... "

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