The World’s Largest Plant Is a Self-Cloning Sea Grass in Australia

In Shark Bay, the ocean floor is carpeted with sea grass, which is undulating in the current and being eaten by dugongs. A new study shows that many of the sea grasses are the same plant that has been cloned for about 4,500 years.

The sea grass is not analgae, but a ribbon weed called Posidonia australis. Jane Edgeloe, a University of Western Australia PhD candidate and author of the paper, compares it to a spring onion.

Ms. Edgeloe and her colleagues SCUBA dived in the shallow waters of Shark Bay and pulled up shoots of Posidonia from 10 different meadows, as part of a genetic survey of Posidonia grasses. The grasses were analyzed and compared.

The results were published in the journal. Many of the plants were almost identical. Elizabeth Sinclair, an author of the study and a researcher at the University of Western Australia, recalled excitement in the lab when she realized it was only one plant.

Posidonia clones itself by creating new shoots that branch off from its root system, unlike the northern meadow which reproduces sexually. The genetically identical meadows were once connected by roots. The Shark Bay clone is about 4,500 years old, based on how old the bay is and how quickly sea grasses grow.

The grass seems to be a hybrid of two species and has two complete sets of chromosomes, a condition called polyploidy. Polyploidy can be helpful in plants. It can result in sterility, as the grass does not flower and can only reproduce by continuing to clone itself.

During a period of ancient climate change, the combination of extra genes and cloning might have been the key to the grass's survival. The ability to cope with a broad range of conditions is a great thing in climate change.

Image

The Shark Bay Posidonia spread even after it survived the climate shift. And spread. Spread some more.

It is the world's largest living creature. Utah's Pando, a colony of 40,000 aspen trees connected by their roots, is the largest individual plant in the world. There is a web of mycelial tendrils underground and beneath tree bark in the Malheur National Forest. The Shark Bay clonal sea grass is about the size of Cincinnati.

The question of whether the Shark Bay clone would be able to survive modern climate change has remained. Julia Haren was not involved in the study, but she praised it for trying to understand why polyploidy has been beneficial.

The University of Gothenburg in Sweden has a biologist who is not involved with the study who says sea grasses are important to protect. She said that they are similar to coral reefs in that they host a lot of other species, along with purifying water and storing atmospheric carbon.

While the stakes are high for sea grasses, Dr. Sinclair remains hopeful that the Shark Bay Posidonia will maintain its status as the world's largest living plant.