Specializes in forest fungi of Rocky Mountains and southwestern U.S.; Phoradendron of U.S. and northern Mexico; Arceuthobium worldwide. The collection includes 4622 accessions of fungi from western North America collected 1890 to 1960 that represent fungi causing tree diseases and wood decays. Founded in 1952. Currently housed in the RMRS in Flagstaff, Arizona. Contains an estimated 12,000 specimens.