Scientists Discover The World’s Largest Plant

Posidonia oceanica, a close “sibling” of Poseidon’s ribbon weed. (Photo: Frédéric Ducarme/Wikimedia Commons) Australia’s colorful Shark Bay is home to a wide variety of sea creatures, like loggerhead turtles, sponge gardens, and yes, sharks. It’s also home to the world’s largest plant: a meadow of self-cloning seagrass as big as the city of Cincinnati. 

The plant is called Posidonia australis, or Poseidon’s ribbon weed, and it looks like an underwater lawn. Jane Edgeloe, a PhD candidate at the University of Western Australia, discovered the meadow’s unique form of reproduction during a genetic survey involving Shark Bay’s various seagrasses. Edgeloe and a few colleagues retrieved samples of Posidonia from ten different locations in Shark Bay, then ran a genetic analysis to compare the species’ DNA. But there wasn’t much to compare: the samples were genetically nearly identical. In fact, they all came from the same plant.

Poseidon’s ribbon weed is a polyploid, meaning its cells each contain more than one pair of chromosomes. This has enabled the plant to reproduce asexually by growing new shoots that stem from its central root system. Since taking form in the shallow waters at Shark Bay approximately 4,500 years ago, Poseidon’s ribbon weed has been undergoing whole-genome duplication at its own pace, no “mate” needed. The only caveat is that it can only continue to reproduce in this way; the plant is unable to flower. 

Shark Bay. (Photo: Simon Maisch/Unsplash)

Edgeloe and her colleagues believe this has given the 180-square kilometer plant the ability to withstand the “temperate and tropical extremes of climate change and extreme weather events, such as marine heatwaves and cyclones.” As she and her co-authors write in the journal Proceedings of the Royal Society B, Poseidon’s ribbon weed managed to survive an Australian heatwave between 2010 and 2011, in which Shark Bay’s surface temperature jumped by more than three degrees Celsius. While more than 1,310 square kilometers of temperate seagrasses were killed off by the heatwave, only a small portion of Poseidon’s ribbon weed were affected—and much of what was killed off has since grown back. 

The plant’s resilience “makes it the most widespread known clone on earth,” writes Edgeloe’s team. A clonal colony of an individual male aspen tree in Utah named Pando would appear capable of taking this title; after all, its 108-acre span is breathtaking. But that’s less than half a square kilometer, meaning Pando pales in comparison with Edgeloe’s discovery. 

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