Armillaria solidipes (formerly Armillaria ostoyae) is a species of fungus in the Physalacriaceae family.
its is spread 2200 acres in US
It is known to be one of the largest living organisms, where scientist 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. Armillaria solidipes grows and spreads primarily underground and the bulk of the organism lies in the ground, out of sight. Therefore, the organism is not visible to anyone viewing from the surface. It is only in the autumn when this organism will bloom “honey mushrooms”, visible evidence of the organism lying beneath. Low competition for land and nutrients have allowed this organism to grow so huge and become the largest living organism.