It was always there, under a shallow blanket of ocean off the Australian coast, but it was believed to be a large meadow of Posidonia, with thousands of individuals. However, a recent genetic study to elucidate how many types of flora there were in that 200 km2 area gave a result that surprised scientists. It was a single, very long, although fragmented, specimen of ‘Posidonia australis’. Thanks to research carried out by researchers from the University of Western Australia (UWA) and Flinders University, it is now known that the world’s largest plant occupies an area similar to that of 28,000 professional football fields.
The work carried out by an Australian student, Jane Edgeloe, sought to find out the genetic richness of this enormous, green sea meadow in Shark Bay. Once the ten samples taken in different parts of this aquatic grass were collected, they were crossed with 18,000 genetic markers. The investigation team expected to find several fingerprints. However, “there was only one!” exclaims Edgeloe in a UWA statement. “That’s it, just a plant that spreads over 180 km, making it the largest known plant on Earth.”
In addition to being gigantic, it would also be the longest-lived vegetable. With these same results, scientists calculate that it is about 4,500 years old, as published in the journal ‘Proceedings of the Royal Society. Biological Sciences’. The genetic study also revealed that it is a plant with double the usual chromosomes, which allows it to live in extreme conditions, such as high temperatures and strong saline concentration. Although they are usually sterile, they grow constantly, as is the case of the Posidonia analyzed.
The scientific question
The most relevant aspect for scientists is the discovery of “a single polyploid clone”, which would have certified that it is a single plant, they explain in the article published on June 1. Polyploidy, common in flowering plants, “has the potential to allow organisms to outcompete their diploid parents.” This also explains the enormous size of the specimen: “the duplication of the complete genome through polyploidy, combined with clonality, may have provided the mechanism for the plant to expand into new habitats and adapt to new environments that became increasingly increasingly stressful for their parents.
This genetic quality, which duplicates chromosomes, is considered an “evolutionary dead end” that can “create monsters”, as had already been proven in terrestrial species. It is now known that it also plays a role in Posidonia meadows, which “inhabit sea coasts and estuaries throughout the world, except Antarctica”, usually with “broad levels of genetic diversity”. In the case of the Australian seas, this almost solitary Posidonia – it has at least one neighbor of another species – “recolonized the continental shelf.”
The giant Posidonia of Shark Bay clings to large areas of sandy sediments protected from ocean waves, the researchers say. “The shallow, protected environment is ideal for clonal growth and vegetative expansion meadows. “For millennia, shallow coastal banks and thresholds marked by natural carbon sequestration have given it extreme conditions.”
Until now, the size record was held by “an ancient diploid clone of ‘Posidonia oceanica’, discovered in the western Mediterranean”, which is 15 km long. Posidonia meadows “can persist almost indefinitely if left undisturbed, as they depend on vegetative expansion of the horizontal rhizome, rather than sexual reproduction,” the article concludes.