A re-examination of generic concepts of baeomycetoid lichens based on phylogenetic analyses of nuclear SSU and LSU ribosomal DNA

The lichen symbiosis has evolved several times within the fungal kingdom, a lthough the total number of lichenization events leading to extant taxa is still unclear. Two lichenized families, the Icmadophilaceae and Baeomycetac eae have been classified in the Helotiales. Because the Helotiales are pred ominantly non-lichenized, this suggests that these families represent indep endent evolutionary episodes of lichenization from the Lecanorales. As a fi rst step towards understanding the evolution of the lichen symbiosis within this order, we tested recent hypotheses concerning the segregation of lich en genera between the two lichen families. Specifically, we used phylogenet ic analyses of nucleotide sequence data from nuclear small-subunit and larg e-subunit ribosomal DNA to rest the morphology-based hypotheses that Dibaei s is a distinct genus from Baeomyces and that Dibaeis is a member of the Ic madophilaceae rather than the Baeomycetaceae. Phylogenetic analyses of nucl ear SSU rDNA and combined SSU and LSU rDNA data support the hypothesis that Dibaeis is more closely related to Icmadophila than it is to Baeomyces. Th erefore, these data support the resurrection of Dibaeis from its previous s ynonymy with Baeomyces based on the characters of ascocarp colour and ascus morphology. The recognition of two distinct genera is also consistent with character state distribution of unique lichen acids. (C) 1999 The British Lichen Society.