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The vast forests of the Pacific Northwest region of the United States, an area outlined by the states of Oregon, Washington, and Idaho, are well known for their rich diversity of macrofungi. The forests are dominated by trees in the Pinaceae with about 20 species in the genera Abies, Larix, Picea, Pinus, Pseudotsuga, and Tsuga. All form ectomycorrhizas with fungi in the Basidiomycota, Ascomycota, and a few Zygomycota. Other ectomycorrhizal genera include Alnus, Arbutus, Arctostaphylos, Castinopsis, Corylus, Lithocarpus, Populus, Quercus, and Salix, often occurring as understorey or early-successional trees. Ectomycorrhizal fungi number in the thousands; as many as 2000 species associate with widespread dominant trees such as Douglas-fir (Pseudotsuga menziesii)(Trappe, 1977). The Pacific Northwest region also contains various ecozones on diverse soil types that range from extremely wet coastal forests to xeric interior forests, found at elevations from sea level to timber line at 2000 to 3000 metres. The combination of diverse ectomycorrhizal host trees inhabiting steep environmental and physical gradients has yielded perhaps the richest forest mycota of any temperate forest zone. When the large number of ectomycorrhizal species is added to the diverse array of saprotrophic and pathogenic fungi, the overall diversity of macrofungi becomes truly staggering.