The ketosynthase domains of putative polyketide synthase (PKS) genes from 15 species in the lichenized genus Lecanora as well as three representatives of other genera were amplified and sequenced using conserved primers. A phylogenetic analysis was carried out with the corresponding amino acid sequences, including those of non-lichenized fungi. The phylogenetic hypothesis places all PKS sequences from Lecanora and the other genera in a clade of PKSs that produce complex aromatic compounds. The PKSs from Lecanora are found in two distinct clades. One of these forms a monophyletic group with PKSs producing precursors of dihydroxy naphthalenes from non-lichenized species. This includes PKSs from the L. rupicola group and several other species which are not closely related. The other clade represents at least one functionally different protein and has no close relationships with known PKSs from other fungi. A comparison between an ITS phylogeny of the species with their DNA sequences of ketosynthase domains reveals similar PKS genes in certain closely related species. Coevolution was unapparent in other clades, suggesting the presence of paralogous genes.