The Australian researchers who discovered the plant set out to map the genetic diversity of the Shark Bay seagrass beds. To their surprise, however, the entire herbarium turned out to consist of a single individual. By continuously making new shoots, the Posidonia distributed over a vast territory. The australians describe their discovery on Wednesday in the magazine Proceedings of the Royal Society B.
“Shark Bay is largely untouched and is located in a fairly sheltered position in the ocean, which means that the plant could continue to grow peacefully“, said researcher Elizabeth Sinclair at the Natural History Museum in London. The plant took a while to grow until it is today: researchers estimate the age of the Posidonia no less than 4,500 years old.
Not two, but four chromosomes
And then the plant has another secret: it does not have two copies of each chromosome, as usual, but four. According to the researchers, the herbarium is an amalgamation of two different parental species. As a result, the plant is genetically equipped for various conditions: more or less salty water, warmer or colder, lighter or darker.
“It’s a very nice discovery,” says Marnel Scherrenberg, head of the botanical collection at the Naturalis biodiversity center. “Until now, the US aspen was the largest known plant. There, an entire forest is made up of genetically identical trees. But this forest was at most 8 kilometers long and this field of seagrass is 180 kilometers.
Scherrenberg even dares to affirm that the Posidonia is the largest known organism. “Animals don’t get that big at all, dinosaurs are eclipsed by that. There are probably huge fungal webs that also consist of a genetically identical individual, but they haven’t been discovered of that size yet.
Successful asexual reproduction
Of Posidonia, which was named after the Greek sea god Poseidon, had long been known to grow very tall. In the western Mediterranean lives a specimen 15 kilometers long, which is believed to be over 100,000 years old.
For biologists, the new discovery also upends the theory of plant reproduction. It has always been thought that the sexual mode of reproduction, in which new genetic combinations are constantly being formed, works best in a changing environment. It now appears that shoot making, or “asexual reproduction”, may be at least as successful.
Biologists’ interest in seagrasses is considerable, as they are capable of shaping entire ecosystems. Seagrasses provide habitat for a range of animal species: from crabs to sea turtles and from fish to dolphins.
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