Largest Plant On Earth Stretches Across 180 Km, Is 4500 Years Old: Australian Researchers

The genes of the plant 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.

New Delhi: Australian researchers have discovered what is believed to be the largest plant on Earth. The ancient and incredibly resilient seagrass is estimated to be at least 4,500 years old and stretches across 180 kilometres. 

Researchers from the University of Western Australia and Flinders University have detailed the discovery of the single plant or 'clone' of the seagrass Posidonia australis in a new study published in the journal Proceedings of the Royal Society B. The clone of Posidonia australis was discovered in the shallow, sun-drenched waters of the World Heritage Area of Shark Bay in Western Australia.

The researchers wanted to understand how genetically diverse the seagrass meadows in Shark Bay were, and which plants should be collected for seagrass restoration, which is when the project began. In a statement released by Flinders University, Dr Elizabeth Sinclair, the senior author on the paper, said the researchers often get asked how many different plants are growing in seagrass meadows, and this time, they used genetic tools to answer the question.

Jane Edgeloe, the lead author on the paper, said the team sampled seagrass shoots from across Shark Bay's variable environments and generated a 'fingerprint' using 18,000 genetic markers. "The answer blew us away — there was just one!" That's it, just one plant has expanded over 180 kilometres in Shark Bay, making it the largest known plant on Earth," Edgeloe further said.

She explained that the existing 200 square kilometres of ribbon weed meadows appear to have expanded from a single, colonising seedling.

Dr Martin Breed, who co-authored the study, said the study presents a real ecological conundrum, which is a confusing and difficult question.

The Largest Plant On Earth Has Seen Its Fair Share Of Environmental Change

He said the single plant may be sterile, and how it has survived and thrived for so long is really puzzling. He added that the plant is not involved in sexual reproduction. Such plants tend to have reduced genetic diversity, which they normally need when dealing with environmental change, he explained.

Breed further said that the seagrass Posidonia australis has seen its fair share of environmental change too. Even today, the plant experiences a huge range of average temperatures from 17 to 30 degrees Celsius. The plant also experiences salinities from normal seawater. Other environmental conditions the seagrass is subjected to include darkness from extreme high light conditions. Despite the fact that these conditions would typically be highly stressful for plants, the seagrass appears to keep going.

How Has The Largest Plant On Earth Survived For So Long?

Breed said that the genes of the seagrass 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.

Sinclair explained that the plant's enormous size, and the fact that it has twice as many chromosomes as its oceanic relatives is what makes it unique from other large seagrass clones. The seagrass plant is a polyploid, the study said.

Sinclair further also said that the whole genome duplication through polyploidy, which refers to the doubling of the number of chromosomes, occurs when diploid 'parent' plants hybridise. Therefore, the new seedling contains 100 per cent of the genome from each parent, rather than sharing the usual 50 per cent.

Sinclair added that polyploid plants often reside in places with extreme environmental conditions, and are often sterile. But they can continue to grow if left undisturbed, and the giant seagrass plant has done just that.

According to Sinclair, the seagrass plant appears to be really resilient even without successful flowering and seed production. It can withstand a wide range of temperatures and salinities, and extreme high light conditions, which together would typically be highly stressful for most plants.

In order to understand how the plant survives and thrives under such variable conditions, the researchers have set up a series of experiments in Shark Bay.