Hiking through the Malheur National Forest in eastern Oregon, you might no- tice a few clusters of honey mushrooms (Armillaria ostoyae) scattered here and there beneath the towering trees (Figure 31.1). Although you might think that the surrounding conifers dwarf the mushrooms, the reverse is actually true. All these mushrooms are just the aboveground portion of a single enormous fungus. Its subterranean network of filaments spreads through 965 hectares of the forest— more than the area of 1,800 football fields. Based on its current growth rate, scien- tists estimate that this fungus, which weighs hundreds of tons, has been growing for more than 1,900 years.
The inconspicuous honey mushrooms on the forest floor are a fitting symbol of the neglected grandeur of the kingdom Fungi. Most of us are barely aware of these eukaryotes beyond the mushrooms we eat or the occasional brush with athlete’s foot. Yet fungi are a huge and important component of the biosphere. While about 100,000 species have been described, there may be as many as 1.5 million species of fungi. Some fungi are exclusively single-celled, though most have complex multicel- lular bodies. These diverse organisms are found in just about every imaginable ter- restrial and aquatic habitat.
Fungi are not only diverse and widespread but also essential for the well-being of most ecosystems. They break down organic material and recycle nutrients