It is known to be one of the largest living organisms, where scientists have estimated a single specimen found in Malheur National Forest in Oregon to have been growing for some 2,400 years, covering 3.4 square miles (8.4 km²) and colloquially named the "Humongous Fungus." Armillaria solidipes grows and spreads primarily underground and the bulk of the organism lies in the ground, out of sight.
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Another "humongous fungus" is a specimen of Armillaria gallica found at a site near Crystal Falls, Michigan, which covered 0.15 square kilometres (37 acres).