Giant Mushroom Largest Living Organism

Aug. 6 -- Walking through the Malheur National Forest in eastern Oregon you would be hard pressed to notice it. But a fungus spreading through the roots of trees now covers 2,200 acres, making it the largest living organism ever found.

Popularly known as the honey mushroom, the Armillaria ostoyaestarted from a single spore too small to see without a microscopeand has been weaving its black shoestring filaments through theforest for an estimated 2,400 years, killing trees as it grows.

“When you’re on the ground, you don’t notice the pattern, youjust see dead trees in clusters,” Tina Dreisbach, a botanist andmycologist with the U.S. Forest Service’s Pacific NorthwestResearch Station in Corvallis, Ore., said Friday.

The outline of the giant fungus, strikingly similar to amushroom, stretches 3.5 miles across, and extends an average ofthree feet into the ground. It covers an area as big as 1,665football fields. No one has estimated its weight.

“There hasn’t been anything measured with any scientifictechnique that has shown any plant or animal to be larger thanthis,” said Gregory Filip, associate professor of integratedforest protection at Oregon State University and an expert inArmillaria.

Dead Trees Reveal Fungus

Until now, the largest known organism was another Armillariaostoyae found in 1992 in Washington State. It covered 1,500 acresnear Mount Adams.

“We just decided to go out looking for one bigger than the lastclaim,” Filip said.

Forest Service scientists are interested in learning to controlArmillaria because it kills trees, Filip said, but they alsorealize the fungus has served a purpose in nature for millions ofyears.

The discovery came after Catherine Parks, a scientist at thePacific Northwest Research Station in La Grande, Ore., in 1998heard about a big tree die-off from root rot in the forest east ofPrairie City, Ore.

Using aerial photos, Parks staked out an area of dying trees andcollected root samples from 112.