The phylogeny of the family Bacidiaceae (Lecanorales, Ascomycota) was investigated using 65 nuclear ITS1-5·8S-ITS2 ribosomal DNA sequences, 63 of which were newly determined. After exclusion of ambiguous alignment, the data set contained 285 variable characters, 212 of which were parsimony-informative. Phylogenetic estimations were performed with maximum parsimony (unweighted and weighted) and maximum likelihood optimality criteria. Four different phylogenetic hypotheses were tested using a parametric bootstrap approach to simulate the expected null distribution of the difference between the globally optimal tree and the best (constrained) tree agreeing with the null hypotheses under unweighted and weighted parsimony, and maximum likelihood: (1) the genus Bacidia is monophyletic; (2) the genus Bacidina is monophyletic; (3) the genus Toninia is monophyletic; and (4) the family Ramalinaceae is monophyletic and distinct from a monophyletic Bacidiaceae. The monophyly of Bacidia, Toninia, and the Ramalinaceae was rejected under all circumstances. Hence, Bacidiaceae is likely to be a younger synonym of Ramalinaceae. The monophyly of Bacidina was not rejected under any optimality criterion. Furthermore, the data set suggests that the Bacidia beckhausii and B. sabuletorum groups are unrelated to Bacidia s. str., that Megalaria is monophyletic, and that Lecania auct. is polyphyletic.