Species related to Buellia aethalea have been examined from the Greater Sonoran Desert Region. In the region, B. aethalea s.str. is a rare montane species. A similar, subalpine species is B. eganii, first reported from New Mexico by R. S. Egan, now validly described here. Most common in the Buellia aethalea-group is B. spuria, a species which does, however, not occur in lowland desert areas of the Sonoran Region. Buellia stellulata is similar to B. spuria, but differs in thallus chemistry and is restricted to areas along the coast. Although similar in thallus morphology, B. lacteoidea is not closely related to the Buellia aethalea-group. The new name, B. maculata, is introduced for the illegitimate B. stigmaea. Buellia maculata is a species with a similar thallus, but not closely related to the Buellia aethalea-group and absent from the North American Southwest. Buellia lepidastra shows some affinities to the group, but like B. maculata is confined to eastern North America.