The largest plant on Earth spans 180 kilometers and is 4,500 years old

The posidonia australis meadow in Shark Bay, Western Australia / U.W.A.

This is a Posidonia australis seagrass located in the shallow, sun-kissed waters of Western Australia's Shark Bay World Heritage Area

EP

Researchers from the Universities of Western Australia (UWA) and Flinders have located what is believed to be the largest plant on Earth, estimating it to be at least 4,500 years old. It is an ancient and incredibly hardy seagrass that stretches for 180 kilometres.

The discovery of this unique seagrass plant or 'clone' Posidonia australis in the shallow, sun-kissed waters of Western Australia's Shark Bay World Heritage Area is detailed in a new study published in the Proceedings of the Royal Society B .

Lead author, evolutionary biologist Dr. Elizabeth Sinclair, of the UWA School of Biological Sciences and UWA Institute of Oceans, says the project began when researchers wanted to understand how genetically diverse seagrass beds were. in Shark Bay and what plants should be harvested for seagrass restoration.

"We are often asked how many different plants grow on seagrass beds and this time we used genetic tools to answer," Dr. Sinclair says in a statement.

UWA student researcher Jane Edgeloe, lead author of the study, says the team sampled seagrass shoots from Shark Bay's variable environments and generated a "fingerprint" using 18,000 genetic markers.

"The answer blew us away: there was only one." Mrs. Edgeloe said. "That's it, just one plant has spread over 180 km in Shark Bay, making it the largest known plant on Earth. The existing 200 km2 of weedy meadows appear to have expanded from a single colonizing seedling."

Flinders University ecologist co-author Dr. Martin Breed was part of the research group. He says the study presents a real ecological conundrum. “In fact, this single plant may be sterile; does not have sex. How it survived and thrived for so long is truly baffling. Plants that don't have sex tend to also have reduced genetic diversity, which they typically need when dealing with environmental change,' says Dr Breed, from Flinders University's School of Science and Engineering.

“Our seagrasses have also seen their fair share of environmental change. Even today, they experience a wide range of average temperatures, from 17 to 30°C. Salinities from normal seawater to double. And from the dark to extreme high light conditions. These conditions are usually very stressful for the plants, but it seems to continue.

Twice as many chromosomes as their oceanic relatives

"As it does? Well, we think its genes are very well adapted to its local, but variable, environment, and it also has subtle genetic differences in its range that help it deal with local conditions,” says Dr Breed.

Dr. Sinclair said what makes this seagrass plant unique from other large seagrass clones, apart from its enormous size, is that it has twice as many chromosomes as its ocean relatives, meaning it is polyploid.

“Whole genome duplication through polyploidy, doubling the number of chromosomes, occurs when diploid 'parent' plants hybridize. The new seedling contains 100 percent of the genome from each parent, instead of sharing the usual 50 percent,” says Dr. Sinclair.

"Polyploid plants often reside in places with extreme environmental conditions, are often barren, but can continue to grow if left undisturbed, and this giant seagrass has done just that.

"Even without successful flowering and seed production, it appears to be very hardy, experiencing a wide range of temperatures and salinities, as well as extreme high light conditions, which together would normally be very stressful for most plants."

Researchers have now set up a series of experiments in Shark Bay to understand how this plant survives and thrives in such variable conditions.

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