Which is the largest living organism by size? Many would answer the blue whale (the largest ocean creature), others the giant sequoia (a tree that typically grows to a height of 70 to 85 metres and five to seven metres in diameter). Many people find it surprising that the largest living organism is a mushroom (!).

The largest living organism is a single gigantic specimen of honey mushroom (Armillaria ostoyae), discovered in the Malheur National Forest, Oregon, USA, in 1998. It occupies a total area of almost 10 square kilometres, equivalent to 1,350 soccer fields, and possibly weighs as much as 35,000 tons, making it the world’s most massive living organism.

The largest living organism is a mushroom

The honey mushroom is well known for its glowing surface, caused by bioluminescent bacteria, although most of its tissue is around one metre underground, in the form of root-like mycelia. Based on its growth rate, its age is calculated to be at least 2,400 years old, but may be as much as 8,650 years old.