It is the largest living organism ever discovered! In the Blue Mountains in Oregon (USA) you can find one of the strangest and oldest organisms discovered on planet Earth, a giant mushroom that would have existed for over 2,400 years. It is an Armillaria ostoyae, which covers approximately 890 hectares, equivalent to 8.900.000 square meters (1.665 football fields), making it the largest organism ever discovered.

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The giant mushroom spreads through the root system of the forest in which it resides and slowly kills all that is on its path, making it not only the largest organism on the planet but also one of the deadliest. For some weeks each autumn, the fungus “explodes” in yellowish clusters with hats, lemellas and spores, but in the rest of the year it takes the form of a thin white layer, similar to latex painting. It is in this less conspicuous form, however, that the fungus is more lethal, as it can spread more easily through the trees.

Trees often benefit from the presence of fungi at their roots, as they help move nutrients through the soil. The Armillaria Ostoyae though. It extends beneath the bark of the trees and causes the roots to rot, slowly sucking life from the tree over the decades. The trees try to fight the parasitic mushroom but they fight an already lost battle.

The mushroom was discovered in 1988 by a forest service employee, Greg Whipple. Initially he thought that the fungus covered “only” 160 hectares, but over time it became clear that it was much larger than that. The forest service dug samples from many areas of the forest, and everywhere they found mushrooms. Initially, they thought it was just the same type of fungus, but further DNA tests revealed that it was actually a single living organism. Experts calculated that, put together, the fungus would have weighed at least 7,500 tons, perhaps up to 35,000 tons.

We have not seen anything else in the literature that suggests anything else in the world is bigger, like a covered surface,” said Greg Filip .

clusters of armillaria ostoyae
Image: Silver Leapers, Flickr

Although it is a fascinating organism, the local timber industry deeply hates this fungus, since it has always stolen their wood, but they have not found an effective way to stop it. In the 1970s, researchers tried to completely eliminate the fungus on different test grounds: they cut trees, dug out logs, and in some areas extracted every fiber they could find. The method produced some results, but the approach was very laborious, expensive and not feasible on a real scale.

Dan Omdal, with the Department of Natural Resources in Washington, is trying another approach: he and his team have planted several species of conifers close to the tree trunk killed by the fungus, with the hope that at least one of the plants will prove tolerant to the mushroom.