This paper reports on a study of the isidiate corticolous species of Caloplaca in North and Central America with notes on similar species from other parts of the world. Of the 20 described isidiate species studied, five are found within the study area. The most common species are C. epiphora and C. furfuracea. Apothecia are frequently found on these isidiate species, in contrast to the sorediate species. A key to all species studied, color photographs, and distribution maps are provided. Several new synonyms are proposed. Caloplaca griseovirens and C. isidiosissima are younger synonyms of Caloplaca aphanotripta. Caloplaca hensseneana and C. neotropica are synonyms of C. wrightii. Caloplaca bassiae and C. herbidella have been reported from the study area, but do not occur here. Caloplaca bassiae is known from Africa, India, China, and Australia and is the oldest name for C. isidiosella and C. malaensis.