If you ever want to pull out the big guns in a pub quiz, then do I have a fact for you! Contrary to popular belief, the biggest organism in the world is not the blue whale. Nor is it the giant sequoia. Nor is it the extinct and admittedly ma-hoo-sive shark, Megalodon. It is… drum roll… a fungus.
Think fungus, think mushrooms, peeping their little domed heads above the leaf litter, but this is only part of the story. Just like an iceberg, the vast majority of the structure is hidden from view.
Mushrooms are the fruiting body of the fungus, like the apples on a tree. These are temporary structures, visible above ground. Most of the fungus, however, is underground in the form of a branching network of tubular filaments called the mycelium.
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Some fungi also have rhizomorphs, which are more specialised, root-like structures. The average supermarket mushroom is just a few inches tall, but the biggest fungus is orders of magnitude bigger.
The biggest fungus, née organism in the world, occupies an area of 3.7 square miles. That’s about the same size as two Gatwick Airports, three Central Parks or four and a half Monacos. Put it another way, the humungous fungus has roughly the same surface area as 18,500 adult blue whales.
Just like New York, this particular variety of fungus is so good, they named it twice. In 1900, the American mycologist Charles Horton Peck called it Armillaria solidipes. Then in 1970, French mycologist Henri Romagnesi dubbed it Armillaria ostoyae, presumably because he never got the memo. Now both names are recognised, but you can call it by its common name, the honey fungus.
The honey fungus grows in North America, where it feeds on trees and spouts mushrooms with honey-brown caps. Its mycelia and rhizomorphs exhibit bioluminescence, which creates a faint green glow known as ‘foxfire’.
The gigantic honey fungus was discovered in 1998, after more than a hundred trees in Oregon’s Malheur National Forest, keeled over and died. A genetic ‘whodunnit’ was launched. Tests revealed that the trees were slain by none other than said fungus, but instead of multiple honey fungi being responsible, the culprit was a single, clonal individual.
Researchers have since worked out how the fungus got so big. A study from 2017 found that the honey fungus has a unique collection of genes that enable it to extend its rhizomorphs miles through the soil in search of wood to eat, and then release enzymes that break down the plant cell walls.
Based on its growth rate, Oregon’s humongous fungus is estimated to be between 2,400 and 8,650 years old, so it’s not just the largest organism in the world. It’s also one of the oldest.
