Joergensenia, a new genus to accommodate Psoroma cephalodinum (lichenized Ascomycota)

The taxonomy of the genus Psoroma (lichenized Ascomycota) is currently under revision, as it has long been recognized as heterogeneous. The aim of the present study was to reconstruct the phylogeny of Psoroma and related genera. The ITS region of nu-rDNA and the mtSSU rDNA from 22 collections of Psoroma and Pannaria were amplified. Sequences from GenBank were also used. For the phylogenetic analysis, direct optimization was implemented, using the program POY, and standard MP using PAUP. Both analyses resulted in similar trees. Two main clades were obtained, one including Santesoniella and most Psoroma species and the other including Pannaria and two Psoroma species, indicating that Psoroma is polyphyletic. Based on its phylogenetic position and ascus type, P. implexum is transferred to the genus Pannaria, and the new combination P. implexa is proposed. Psoroma cephalodinum clusters with Parmeliella and Degelia as a basal group within the Pannariaceae. The ascus apex of P. cephalodinum has a strong amyloid reaction revealing a compact cap-shaped plug. This differs from most of the ascus apical structures observed in the family. Both ascus internal structure and phylogenetic position suggest that P. cephalodinum is distantly related to Psoroma or Pannaria, and thus a new genus Joergensenia is proposed.