This May Be Earth's Largest Organism

A single Posidonia australis seagrass covers 77 square miles off western Australia
By Arden Dier,  Newser Staff
Posted Jun 1, 2022 12:52 PM CDT
Updated Jun 5, 2022 1:30 PM CDT
This Plant Is as Big as 20K Football Fields
The Posidonia australis seagrass in Shark Bay.   (Rachel Austin/University of Western Australia)

Scientists have discovered what is arguably the world's largest living organism, which is roughly the size of 20,000 football fields and about 4,500 years old. It's a seagrass known as Poseidon's ribbon weed, or Posidonia australis, which started as a seed spawned from two different species. Nestled in Shark Bay off the westernmost tip of Australia, it slowly grew to become the biggest plant on Earth, covering over 77 square miles "or just over three times the size of Manhattan island," per the Guardian. Scientists only discovered it when looking for genetic differences in ribbon weed over a large area. Hoping to find specimens to use in restoration, they examined 18,000 genetic markers in various samples.

This showed 116 samples taken up to 110 miles apart were from a single plant. "We thought 'what the hell is going on here?'" Dr. Martin Breed, an ecologist at Flinders University, tells the Guardian. It turns out this ribbon weed is expanding up to 14 inches each year through clone offshoots. Given the size of the current underwater meadow—a home to dolphins, dugongs, turtles, and crabs—this plant must be at least 4,500 years old, scientists say. That's not so unbelievable. Other genetic studies have shown seagrass can live between 2,000 and 100,000 years. Though patchy, this specimen is particularly hardy, surviving in areas of Shark Bay where the salt content is double that of other bay locations.

That hardiness is thanks to its makeup: A hybrid of two species, it has two complete sets of chromosomes—a condition known as polyploidy, per the New York Times. As evolutionary biologist Dr. Elizabeth Sinclair of the University of Western Australia puts it to the Guardian, "Instead of getting half [of] its genes from mum and half from dad, it's kept all of them." This has "essentially doubled the genetic diversity in the plant, likely increasing its ability to tolerate a wider range of environmental conditions," Sinclair, an author of the study published Wednesday in Proceedings of the Royal Society B, tells Live Science. It may also have resulted in the plant being largely sterile. Only its northern meadows reproduce sexually, per the Times. The remainder has to grow by sending new shoots out of its root system. (Read more discoveries stories.)

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