One of the Oldest, Largest Living Things on Earth Is an Underground Mushroom in the U.P.

Quick — what is the biggest living thing on the planet? Most people guess a blue whale or a giant sequoia. For a brief stretch in the early 1990s, a fungus near Crystal Falls was part of that argument.

Beneath a forest near Crystal Falls, in the western Upper Peninsula, lives a single organism known affectionately as the “humongous fungus.” It’s an Armillaria gallica — a honey mushroom — and it isn’t one of the little caps you see popping up after rain. Those caps are just the tips. The real organism is a vast underground web of black, root-like threads spreading through the soil, all of it a single connected individual.

Scientists began mapping the individual in the late 1980s. In a 1992 Nature paper, they reported a minimum area of 15 hectares, or about 37 acres. They estimated that it weighed more than 10,000 kilograms — roughly 11 U.S. tons — and had remained genetically stable for more than 1,500 years. That was enough for the researchers to call fungi some of Earth’s oldest and largest organisms.

The team returned with wider sampling and whole-genome tools for a 2018 study. That work put the same individual at about 75 hectares, or roughly 185 acres. The revised estimates were at least 2,500 years old and about 400,000 kilograms — roughly 440 U.S. tons.

It is not the current size record holder; a larger Armillaria individual is known in Oregon. Crystal Falls kept the better nickname, though, and the town still throws an annual festival in its honor. The fungus itself remains mostly out of sight, which may be the most fitting part of the story: one of Michigan’s largest residents is almost entirely underground.