The lichenicolous fungus Sphaerellothecium taimyricum is reported as new to North America. The lichenicolous fungus Lichenopeltella leprosulae and the lichen Protothelenella leucothelia are reported as new to the USA and the hepaticolous fungus Pleostigma jungermannicola is reported as new to western North America. Arthonia xanthoparmeliarum is reported as new to northwestern North America and seven other species of lichenicolous fungi are reported as new to the contiguous 48 states of the USA. In total, 18 species are reported new to the state of Washington, 2 to California and Oregon, and one new species is reported for each of three other western states. Key words. Arthonia, biodiversity, Llimoniella, Phaeophyscia, Washington, Whatcom County.