This Giant Mushroom is the Armillaria solidipes, formerly Armillaria ostoyae
A mushroom of this type in the Malheur National Forest in the Strawberry Mountains of eastern Oregon, U.S. was found to be the largest fungal colony in the world, spanning 8.9 square kilometres (2,200 acres) of area. This organism is estimated to be 2,400 years old.
The fungus was written about in the April 2003 issue of the Canadian Journal of Forest Research. While an accurate estimate has not been made, the total mass of the colony may be as much as 605 tons. If this colony is considered a single organism, then it is the largest known organism in the world by area, and rivals the aspen grove “Pando” as the known organism with the highest living biomass. In 1992, a relative of the Strawberry Mountains clone was discovered in southwest Washington state. It covers about 6 square kilometres (1,500 acres).
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Strange but True: The World’s Largest Organism is a Giant Mushroom https://bookofresearch.wordpress.com/2015/03/18/strange-but-true-the-worlds-largest-organism-is-a-giant-mushroom/