Context: 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.

Seagrass

• These are flowering plants that grow submerged in shallow marine waters like bays and lagoons.
• These have tiny flowers and strap-like or oval leaves.
• Sea grasses evolved from terrestrial plants that colonised the ocean 70-100 million years ago
• Like terrestrial plants, seagrasses also require sunlight for photosynthesis from which these manufacture their own food and release oxygen.

Key Importance

• Seagrasses can capture carbon from the atmosphere up to 35 times faster than tropical rainforests.
• Help maintain water quality by trapping fine sediments and suspended particles in the water column and increase water clarity.
• Filter nutrients released from land-based industries before they reach sensitive habitats like coral reefs.
• Prevent soil erosion as the extensive vertical and horizontal root systems of seagrasses stabilise the sea bottom.
• Provide food as well as habitat for fishes, octopuses, shrimp, blue crabs, oysters, etc.
• Endangered marine organisms like dugong (Sea Cow), green turtle, etc, graze directly on seagrass leaves.

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.