Researchers from two Australian universities have discovered what they believe to be the largest plant in the world, an ancient and resilient seagrass that stretches 180 kilometres across.
This single giant plant of the seagrass Posidonia australis is estimated to be 4,500 years old. It was found in the shallow waters of Shark Bay in Western Australia (WA) and has been detailed in a study published in the journal Proceedings of the Royal Society B.
Dr Elizabeth Sinclair, a senior author of the study and evolutionary biologist from the University of WA’s (UWA) School of Biological Sciences and the UWA Oceans Institute, said researchers were initially looking into how genetically diverse the seagrass meadows in Shark Bay, Western Australia were, as well as which plants should be collected for seagrass restoration.
“We often get asked how many different plants are growing in seagrass meadows, and this time we used genetic tools to answer it,” she said in a release on Wednesday.
UWA student researcher and lead author of the study, Jane Edgeloe, said their team sampled seagrass shoots from across the bay and came up with a fingerprint using 18,000 genetic markers.
“The answer blew us away—there was just one!” she said. “That’s it, just one plant has expanded over 180 kilometres in Shark Bay, making it the largest known plant on earth.”
“The existing 200 kilometres of ribbon weed meadows appear to have expanded from a single, colonising seedling,” she added.
Ecologist and co-author of the study Dr. Martin Breed of Flinders University, South Australia, said the study presented an ecological conundrum.
“The plant may be sterile, so if it doesn’t have sex, how it has managed to survive and thrive for so long is puzzling,” he said, stressing that plants that don’t have reproduction tend to have reduced genetic diversity, something they normally need when facing environmental change.
“Our seagrass has seen its fair share of environmental change too. Even today, it experiences a huge range of average temperatures, from 17 to 30°C, salinities from normal seawater to double that, and from darkness to extreme high light conditions,” Breed said.
“These conditions would typically be highly stressful for plants. Yet, it appears to keep on going.
“How does it do it? Well, we reckon its genes are very well-suited to its local, but variable, environment, and it also has subtle genetic differences across its range that help it deal with the local conditions,” he said.
Sinclair said this seagrass plant is set aside from other large seagrass clones because it contains twice as many chromosomes as its relatives, making it a polyploid.
A polyploid is an organism that contains more than two complete sets of chromosomes. According to Study.com, plants are more commonly polyploids as they lack separate sexes and are able to self-pollinate, although some fish and amphibians, as well as invertebrates such as leeches and flatworms, are also polyploids.
“Whole genome duplication through polyploidy—doubling the number of chromosomes—occurs when diploid ‘parent’ plants hybridise. The new seedling contains 100 percent of the genome from each parent, rather than sharing the usual 50 per cent,” Sinclair said.
“Polyploid plants often reside in places with extreme environmental conditions, are often sterile, but can continue to grow if left undisturbed, and this giant seagrass has done just that.”
The team of researchers is now conducting a series of experiments to understand how the Shark Bay Posidonia australis survives and thrives in the challenging conditions.