Three hypotheses of the phylogeny of the lichenized Parmeliaceae are constructed, using sequences of the nuclear ribosomal gene cluster (SSU, ITS, 5·8S rDNA) from Bryoria capillaris, Cetraria islandica, Evernia prunastri, Hypogymnia physodes, Parmelia saxatilis, Platismatia glauca, Pleurosticta acetabulum, Usnea florida, Vulpicida juniperina, V. pinastri and Xanthoparmelia conspersa. The first analysis, based on SSU sequences, shows the representatives of the Parmeliaceae to form a monophyletic group within the order Lecanorales. Usnea florida and Bryoria capillaris, sometimes classified in the families Usneaceae and Alectoriaceae, respectively, are also members of the Parmeliacceae. Cetraria and Vulpicida form a well-supported monophyletic group together with Usnea, but there is little support for any other groupings within Parmeliaceae. The second analysis is based on ITS an 5·8S sequence data of the representatives of the Parmeliaceae included in the first analysis, and supports the close relation of Cetraria and Vulpicida. Other groupings are not supported, and the topology also varies greatly with minor alignment changes. This is attributed to the included taxa being too distantly related to each other, causing alignment difficulties of the variable ITS region when a relatively small number taxa are included. It is predicted that a larger sample of phylogenetically intermediate taxa will overcome this problem. When combining the two datasets, the results are similar to the ITS results. The present study is one of the first phylogenetic studies utilizing the information in more than one gene alone in lichenized ascomycetes.