About 4,500 years ago, a single seed — bred from two different types of seaweed — found itself nestled in a niche somewhere in what is now Shark Bay, off the western coast of Australia.
Left to their own devices and relatively undisturbed by human hands, the seeds grew into what is now believed to be the largest plant anywhere on Earth, covering about 200 square kilometers (77 square miles, or about 20,000 rugby fields, or just over about three times the size of Manhattan Island).
Species – A Posidonia australisalso known as fiber ball weed or tape weed – is most commonly found along the southern coasts of Australia.
But when scientists began looking for genetic differences in tape weeds across the bay, they came across a mystery. Samples taken from sites that are 180 km apart, suggest that there are not several samples of Posidonia australis, But one plant.
“We thought ‘What the hell is going on here?'” said Dr. Martin Breed, an ecologist at Flinders University. “We were confused.”
Student researcher Jane Idjello from University of Western part of Australia (UWA), about 18,000 genetic markers were examined as they searched for species differences that might help them select samples for use in restoration projects.
Instead, what they found was that the plant itself propagated using roots in the same way that grass can spread from its edges by sending out runners.
“It appears that the existing 200 square kilometer ribbon weed meadows have expanded from a single colonial seedling,” she said.
The lone plant now spreads out like meadows, providing a home to a wide range of marine species including turtles, dolphins, dugongs, crabs, and fish.
Tape weed roots can grow up to 35 cm per year, and at this rate, the authors search – Published in Proceedings of the Royal Society B – Estimated that the plant would need at least 4,500 years to spread as far as it is.
They did not give the plant a nickname, said Dr Elizabeth Sinclair, a co-author on the research at the University of Western Australia, and that the original samples – taken from a seagrass meadow – originally had 116 different labels with GPS coordinates when they were stored at depths. Freeze-ready for genetic sampling.
The plant forms huge, dense lawns that extend in some areas as far as the eye can see in all directions. The strips of the plant are only 10 cm long in some places, but up to a meter in others.
Conditions at Shark Bay itself are tough. The plant has found a way to survive in areas where salinity is twice that of elsewhere in the bay, and can thrive in water temperatures of up to 15°C and hots of up to 30°C.
Sinclair said the survival of the seaweed plant appears to be related to how it retains all of its chromosomes from its parents, giving it endogenous genetic diversity.
“Instead of getting half [of] Her genes are from my mom and half from my dad, she kept them all,”
Sinclair and her colleagues are still working through the secrets of the giant specimen, but she said it appears “pretty sterile” and so has to rely on its ability to grow, rather than scatter the seeds.
The fact that the plant “doesn’t have sex” but survived for so long was a mystery, Breid said.
“Sexless plants also tend to have less genetic diversity, which they typically need when dealing with environmental change,” he said.
Breed said they discovered some subtle mutations in the plant’s genes across the places where it was growing that may also explain its extreme longevity.
The Shark Bay strip grass has a size of about 20,000 hectares (49,000 acres)—much larger than a stand of shaky aspen trees in Utah, It is often referred to as the largest factory in the worldcovering 43 hectares.
Associate Professor Catherine McMahon, from Edith Cowan University, was not involved in Shark Bay’s research but is an expert in seaweed. She said the method the researchers used gave her confidence that they had identified one sample, which she said was “amazing.”
Genetic studies of other seaweed species have estimated that plants can live between 2,000 and 100,000 years, so McMahon said the estimate that the Shark Bay sample was 4,500 years old fits that range.
“They have a versatile growth pattern that contributes to this long life,” she said. “They can grow toward nutrient-rich patches to get the nutrients they need, into gaps in a lawn where there is room to grow or away from stressed places.
“All of these properties mean that if they are in the right place they can last for long periods of time.”