Next time you purchase white button mushrooms at the grocery store, just remember, they may be cute and bite-size but they have a relative out west that occupies some 2,384 acres (965 hectares) of soil in Oregon's Blue Mountains. Put another way, this humongous fungus would encompass 1,665 football fields, or nearly four square miles (10 square kilometers) of turf.
The discovery of this giant Armillaria ostoyae in 1998 heralded a new record holder for the title of the world's largest known organism, believed by most to be the 110-foot- (33.5-meter-) long, 200-ton blue whale. Based on its current growth rate, the fungus is estimated to be 2,400 years old but could be as ancient as 8,650 years, which would earn it a place among the oldest living organisms as well.
A team of forestry scientists discovered the giant after setting out to map the population of this pathogenic fungus in eastern Oregon. The team paired fungal samples in petri dishes to see if they fused (see photo below), a sign that they were from the same genetic individual, and used DNA fingerprinting to determine where one individual fungus ended.
This one, A. ostoyae, causes Armillaria root disease, which kills swaths of conifers in many parts of the U.S. and Canada. The fungus primarily grows along tree roots via hyphae, fine filaments that mat together and excrete digestive enzymes. But Armillaria has the unique ability to extend rhizomorphs, flat shoestringlike structures, that bridge gaps between food sources and expand the fungus's sweeping perimeter ever more.
A combination of good genes and a stable environment has allowed this particularly ginormous fungus to continue its creeping existence over the past millennia. "These are very strange organisms to our anthropocentric way of thinking," says biochemist Myron Smith of Carleton University in Ottawa, Ontario. An Armillaria individual consists of a network of hyphae, he explains. "Collectively, this network is called the mycelium and is of an indefinite shape and size."...
