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The Caloplaca holocarpa group in the Nordic countries, except Iceland, is defined genetically using the nrlTS DNA gene. The members are analysed with regard to morphology, anatomy, ecology, and chemistry. The results show that C. holocarpa seems to be a very small group, but there are many morphologically similar species outside the group. Within the group several species have been confused, but it is shown that C. holocarpa, C. pyracea, and C. vitellinula are separate taxa. Caloplaca cerinella also belongs to the group whereas C. cerinelloides does not, but is included in the treatment because of its similarity to the former species. Caloplaca lithophila H. Magn. is a synonym of either C. holocarpa or C. vitellinula, most probably of the latter. Many specimens determined to C. holocarpa belong to Caloplaca oasis, but this species is shown to have much more variable morphology and wider ecology and distribution than previously understood. Caloplaca oasis has also been confused with C. Polycarpa, which is similar, but morphologically and genetically distinct, even though related. Neither of the two species belong to the C. holocarpa group, but are related to the C. citrina group, not to the C. velana group as usually believed. Other species from northern and central Europe similar to C. holocarpa belong in other groups. The treated species are described and illustrated in colour. Distribution maps are given for the study area. A key to species in northern Europe similar to C. holocarpa is also provided.