The honey mushroom (Armillaria ostoyae) is the largest single organism on earth and is found in the Blue Mountains of eastern Oregon in the USA.

Researchers investigated the fungus in 2000, when they realised that it was responsible for killing large groves of evergreen trees. When foresters cut into an infected tree they found spreading white filaments, mycelia, which draw water and carbohydrates from the tree to feed the fungus. Researchers collected samples of the fungus from a widespread area and analysed the DNA. A large sample of the specimens they collected turned out to be from a single organism.

This most recent find was estimated to cover over 2,200 acres (890 hectares) and be at least 2,400 years old.