beta-tubulin, ITS and group I intron sequences challenge the species pair concept in Physcia aipolia and P-caesia

ITS, group I intron and partial beta -tubulin sequences were used to infer phylogenies of a putative lichen species pair: Physcia aipolia (sexual) and P. caesia (asexual). A jackknife tree obtained from the beta -tubulin sequ ences produced a well-resolved tree, whereas the resolution in the group I intron and in the ITS tree was lower due to homoplasy. The results obtained from the combined group I intron, ITS and beta -tubulin data indicate that neither P. caesia nor P. aipolia are monophyletic and suggest that the two taxa are conspecific. Although the combined DNA data suggest the existence of several genetically isolated lineages in the P. aipolia/caesia group, t he different lineages were not correlated with any morphological characters . Within one of the lineages, the incongruent placement of one I? aipolia s pecimen may indicate sexual recombination. A contradictory placement of one P. caesia specimen in different trees suggests that the usually asexual P. caesia is occasionally capable of sexual reproduction. The beta -tubulin g ene was found to contain enough variation for inferring relationships at th e species level. Most of the informative characters were found from intron sequences and third codon positions in the exon regions. All the nucleotide substitutions were synonymous.