October 05, 2007

It's Big, It's Old, and It Eats Trees for Breakfast

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...

"People had ideas that maybe they were big but nobody had any idea they were that big," says Tom Volk, a biology professor at the University of Wisconsin–La Crosse. "Well it's certainly the biggest publicity that mycology is going to get—maybe ever."


Tom Volk, by the way, is particularly expert in all things Armillaria, having described several species himself with work he did on mating strains a few years back.

It is amazing to most people to think that "mushrooms" can get as big as this, mostly because they think of mushrooms as an organism instead of as an organ. A mushroom is to a fungus as a flower is to a tree, and nobody is surprised that trees can be very large because their flowers are small. If anything, the "humongous fungus" and its kin may only be the tip of the iceberg in terms of size, simply because we don't know quite where to look for even more massive organisms. There are probably mycelia of Mycena, for example, that undergird entire forests, even though their sporocarps are smaller in diameter than pennies and might not appear as regularly as Armillaria. The honey mushrooms are uncannily regular in their appearance year after year and you could probably establish a fairly accurate calendar based on what day a particular cluster of them will appear in a particular locale. For these reasons, Armillaria are among the most conspicuous of fungi. Tiny Mycena, Collybia and Coprinus aren't quite so dependable in fruiting, but this doesn't really mean anything in terms of what's happening on and under the forest floor.

Let's face it... it's all about the fungus. We primates are lucky they didn't decide in large numbers to make us their substrate of choice. If our nitrogen and phosphorus contents were a bit higher, they very well might have... and then we'd look like this unfortunate creature:

There is, indeed, a group of sporocarp-forming fungi that have settled on insects as their favorite source of nutrition. The fly above is being consumed by one of them, Cordyceps dipterigena.

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