Ancient plants appear to have spread from a single seedling (Photo: Rachel Austin)

Researchers have discovered the world’s largest plant, about the same length as the distance between London and geese.

The plant is an ancient and incredibly strong seagrass that stretches for 180 km and is estimated to be at least 4,500 years old.

Scientists have discovered the plant in the shallow, sunny waters of Shark Bay, Western Australia, a World Heritage Site.

One plant in 200 square kilometers of tapeworm meadows is actually a “clone” of the algae Posidonia australis, which appears to have spread from seedlings to form a single colony.

The findings were produced by researchers from the University of Western Australia (UWA) and Flinders University. They published the findings in the proceedings of the Royal Society B.

The project began when researchers wanted to know how genetically diverse the seagrasses in Shark Bay were and what plants needed to be collected to restore the seagrasses.

Seaweed

Scientists have discovered plants in the shallow, sunny waters of Shark Bay in Western Australia (Photo: Angela Rosen).

“I’m often asked how many different plants grow in kelp beds, but this time I used genetic tools to answer that,” said Dr. Elizabeth Sinclair, an evolutionary biologist at UWA and lead author of the study.

Jane Egero, lead author of the study, said the team sampled seagrass shoots from different shark environments and used 18,000 genetic markers to create “fingerprints.”

“The answer surprised us, there was only one!” Egeroe said. “That’s it. Just one plant in Shark Bay has expanded to 180km, making it the most famous plant on the planet.”

Aside from its large size, this alga differs from other large algae clones in that it has twice as many chromosomes as its marine counterparts. In other words, it is a polyploid.

Complete duplication of the genome with ploidy (doubling of chromosome number) occurs during mating of diploid “parent” plants. “The new seedlings contain 100% of the genome from each parent, instead of the usual 50%,” says Dr. Sinclair.

Polyploid plants often inhabit areas with extreme environmental conditions and are often barren, but they can keep growing if they don’t mind, and this giant seagrass did just that.

Even with unsuccessful flowering and seed production, the plant is strong, resistant to a wide range of temperatures and salt, and has very high light conditions. These are usually very stressful for most plants.

Researchers are currently conducting a series of experiments in Shark Bay to see how the plant survives and thrives in these changing conditions.