The world’s largest plant has recently been discovered off the West Coast of Australia: a seagrass 180 km in length.

Posidonia australis

• The ribbon weed, or Posidonia australis, has been discovered in Shark Bay by a group of researchers from Flinders University and The University of Western Australia.
• These researchers have also found that the plant is 4,500 years old, is sterile, has double the number of chromosomes than other similar plants.
• It has managed to survive the volatile atmosphere of the shallow Shark Bay.

So how remarkable is this plant’s size?

• The ribbon weed covers an area of 20,000 hectares.
• The next on the podium, the second largest plant, is the clonal colony of a quaking Aspen tree in Utah, which covers 43.6 hectares.
• The largest tree in India, the Great Banyan in Howrah’s Botanical Garden, covers 1.41 hectares.

If it is so large, how come it has just been discovered?

• The existence of the seagrass was known, that it is one single plant was not.
• Researchers were interested in what they then thought was a meadow because they wanted to study its genetic diversity, and collect some parts for seagrass restoration.

How did it grow, and survive for, so long?

• Sometime in the Harappan era, a plant took root in the Shark Bay.
• Then it kept spreading through its rhizomes, overcoming everything in its way, and here we are today.
• Ribbon weed rhizomes can usually grow to around 35cm per year, which is how the scientists arrived at its lifespan of 4,5000 years.
• The researchers found that the ribbon weed cannot spread its seeds, something that helps plants overcome environmental threats.
• Also, Shark Bay sees fluctuations in temperature and salinity and gets a lot of light, conditions challenging for any plant.

Ecological significance

• Because seagrass performs a vital role in the environment, and if some of it is hardy, it is good news for everyone in a world threatened by climate change.
• In India, seagrass is found in many coastal areas, most notably in Gulf of Mannar and Palk Strait.
• Apart from being home to a variety of small organisms, seagrass trap sediments and prevent water from getting muddy, absorb carbon from the atmosphere, and prevent coastal erosion.

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