The largest living organism ever found has been discovered in an ancient American forest. The Armillaria ostoyae, popularly known as the honey mushroom, started from a single spore too small to see without a microscope. It has been spreading its black shoestring filaments, called rhizomorphs, through the forest for an estimated 2,400 years, killing trees as it grows. It now covers 2,200 acres (880 hectares) of the Malheur National Forest, in eastern Oregon. Do you think it exists ?