There are seagrasses and older land plants in other parts of the world, but none are thought to be as large as this one. Aquatic ribbon grass covers approximately 200 square kilometers of Shark Bay in Western Australia and was hidden in plain sight . In fact, it was long believed to be a collection of distinct plants, but tests have revealed that, genetically speaking, it is a single entity: a single, enormous Posidonia australis plant, which began life some 4,500 years ago when Ancient Egyptians built the pyramids of Giza.
A gigantic network of seagrasses
The meadow web is essentially a single plant that has grown from a single “colonizing” seedling with long, bright green ribbons that has been cloning itself for thousands of years.
The researchers used genetic tools to address the question of how many different types of plants lived in the shallow waters of Western Australia, specifically in the Shark Bay area. They collected samples of seagrass shoots from various habitats throughout the region and examined 18,000 genetic markers to create profiles of the plants.
What they discovered was a pleasant and great surprise:
“The answer blew us away: there was only one!” said Jane Edgeloe, a student researcher at the University of Western Australia and lead author of the study published in the journal Proceedings of the Royal Society B: Biological Sciences . “That’s it, just one plant has spread over 180 km in Shark Bay, making it the largest known plant on Earth. The existing 200 square kilometers of weedy meadows appear to have expanded from a single colonizing seedling .
Beyond this record, the huge plant baffles scientists as its lack of a sexual life means it would be expected to have limited genetic diversity, leaving it vulnerable to environmental change, but it doesn’t. According to experts, the plant contains twice as many chromosomes as its oceanic relatives, which indicates that it is polyploid and hence has good tolerance to the temperature extremes that the area supports (from 17 to 30 °C).
“Whole genome duplication through polyploidy, doubling the number of chromosomes, occurs when diploid ‘parent’ plants hybridize. The new seedling contains 100 percent of the genome from each parent, instead of sharing the usual 50 percent,” said co-author Elizabeth Sinclair.
Referencia: Jane M. Edgeloe et al, Extensive polyploid clonality was a successful strategy for seagrass to expand into a newly submerged environment, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.0538
