©NRCan

In Oregon’s Blue Mountains, patches of dying trees once looked like separate outbreaks, scattered across ridges and drainages as if disease had struck at random. Instead, scientists found something far stranger beneath the soil: many of those distant pockets belonged to the same fungus. That fungus, Armillaria ostoyae, covered about 9.65 square kilometers, making it the largest known individual fungus on Earth at the time of the study. It had likely been growing there for at least 1,900 years, and possibly as long as 8,650. For researchers, the discovery did more than set a record. It challenged a basic biological idea: what counts as an individual. “It’s one organism that began as a microscopic spore and then grew vegetatively, like a plant,” said Dr. Catherine Parks, a research plant pathologist with the U.S. Department of Agriculture Forest Service and coordinator of the team.