This is the largest plant in the world, and it measures 180km

This is the largest plant in the world, and it measures 180km

Abstract Aerial Art via Getty Images

Sea view of seagrass beds in Shark Bay, Western Australia.

BIODIVERSITY – These bright green ribbons ripple to the rhythm of the currents, and form true meadows in the sea. These are marine herbs, which are not algae, but flowering plants, which bear fruit every year.

To find out the number and diversity of these “sea meadows”, a study published in the June 1 issue of the journal Royal Society tested their DNA. Specifically, the researchers went to take samples of the plant Posidonia australis between 2012 and 2019 in 10 different marine herbariums. These are located in the shallow, sunny waters of Shark Bay. on the west coast of Australia.

And the result was surprising to say the least: it was actually a single plant. More precisely, it is a single plant plant that has grown over 180 km (the distance between Paris and Auxerre), reproducing and “cloning” on a scale never seen before these seaweeds.

A 4500 year old planting grandfather

Shark Bay, formerly a simple sand dune, was submerged about 8,500 years ago; the sea level engulfed her at the end of the ice age. If it remains difficult to determine the exact age of these marine herbivores, they would be approximately 4,500 years old based on their size and growth rate.

As it grew, the seagrass beds shaped the reef, creating real sea fields. This demonstrates the resilience of these plants, as the waters of Shark Bay are bathed in strong light, low nutrient levels, and large temperature fluctuations.

In addition to its gigantic size, what makes this plant unique comes from its chromosome number, which is twice as large as its parents. Researchers call this plant a “polyploid.” Usually, a herbarium inherits half of the genome of each of its parents, but here it bears the whole of both parents. Potatoes or bananas are also part of this family, which usually resides in extreme environmental conditions.

Resistant to climate change

If other organisms like corals are very fragile in the warming and acidification of the oceans, marine herbivores hold up better. How do they accomplish this feat? This is all the more surprising given that these plants, and more broadly polyploids, are often sterile. Strange while reproducing sexually is the best option to adapt. Indeed, the sex and the offspring that come from it allows foster genetic diversityincreasing the ability to cope with changing environments.

Angela Rossen / TheConversation

Photo of flowers of the marine plant Posidonia australis.

But it’s not just sex in the lives of these marine herbivores that is developing in a second way. To grow, they extend their rhizomes, underground stems from which new shoots emerge. Another benefit is that the Shark Bay herbarium has somatic mutations (minor genetic changes) that allow it to be extremely well adapted to its local environment, despite its variability.

Indeed, the waters of this bay can vary between 17 and 30 degrees in temperatures, while the level of salinity can go from single to double. Nevertheless, the researchers point out that experiments need to be conducted to truly understand how this plant succeeds in this feat. This is especially in order to protect her because, if he resists better, she is not not immune to climate change.

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