One Big Fungus : 40-Acre Growth Found in Michigan Is Called the Largest Living Organism

The world’s largest living organism is neither a California sequoia nor the giant blue whale, but a 40-acre fungus.

Canadian researchers report today in the journal Nature that the humongous fungus lives beneath a forest in the Upper Peninsula of Michigan, according to botanist Myron L. Smith of the University of Toronto in Ontario.

The fungus, a single continuous organism, weighs as much as 220,000 pounds and is apparently 1,500 years old.

By contrast, a great blue whale weighs as much as 250,000 pounds, but occupies much less than an acre of space. And sequoias may weigh as much as 2 million pounds, but most of that is dead wood. Coral reefs, which some argue are the largest living organisms, are also composed mostly of dead material.

Smith and his colleagues have not seen the entire fungus. It lives just below the surface, on and between the roots of hardwood trees. They determined its size by taking samples of it over the 40-acre test site and confirming that all of the samples were genetically identical. If any of the samples had come from another fungus, even an offspring, it would have a slightly different genetic composition.

Although the main body of this fungus, a species called Armillaria bulbosa, is underground, it produces edible outcroppings called honey mushrooms.

The researchers estimated the age of their prize specimen by noting that it expands outward at a rate of about eight inches per year. Based on that growth rate, it is at least 1,500 years old, but if it suffered competition from other fungi or experienced adverse environmental conditions that reduced its growth, it could be much older, Smith said.

The same species lives under hardwood forests throughout eastern North America and Europe, and Smith speculated that there may be others that are even bigger and older.