Humongous Fungus

Watch out, Milwaukee. Something is growing in the woods just over, or rather under, the Wisconsin-Michigan border. It feeds off rotting organic matter and tree roots, and has been doing so for 1,500 years, making it at least half as old as a mature sequoia tree. The thing has already taken over a whopping 15 hectares (37 acres). It weighs in at somewhere between 100 and 1,000 tons, at least as big as a blue whale. And it is still growing. At its present creep, it could reach the city of beer and bratwurst in a mere 1.6 million years.

The consequences will be a plague of mushrooms. That is how many fungi reproduce, and this mass of subterranean cytoplasm, known scientifically as Armillaria bulbosa, is one humongous fungus. The mushrooms are aboveground appendages of the real organism, a tangled mass of stringlike tendrils that spread below the surface. Just how far a given fungus can spread has always been open to speculation. Unless scientists happen to dig right where two clearly different fungi meet, there is no easy way to tell where one ends and another begins.

The Canadian and U.S. scientists who reported the discovery in last week's Nature solved this identity problem with the latest methods of DNA analysis. ; They found that all the samples within the sprawling study area were genetically identical -- meaning they had to be part of one, individual organism.

But just what is meant by an "individual"? A patch of grass that spread from a single seed may be considered an individual organism. The same is true with fungi, which, incidentally, are now looked upon as a kingdom separate from plants and animals. Complicating matters is the fact that pieces of the A. bulbosa may have broken off over the millenniums. If so, do the pieces count as one organism or many? There's no agreed upon answer, says Clive Brasier, a British botanist. Insisting on a yes or no, he says, "gets to be a Guinness Book of Records kind of question."