Arthoniomycetes are a class of ascomycete fungi. It includes the single order Arthoniales. Most of the taxa in this class are tropical and subtropical lichens.
Phylogenetic analysis supports the monophyly of this class. Dothideomycetes is a sister group.
Taxa have apothecia, cup- or saucer- shaped ascoma in which the hymenium is exposed at maturity. These apothecia are bitunicate - with clearly differentiated inner and outer walls.