Evolutionary relationships of nonsexual lichenized fungi:: molecular phylogenetic hypotheses for the genera Siphula and Thamnolia from SSU and LSU rDNA

The nonsexual lichenized family Siphulaceae is comprised of the obligately sterile genera, Siphula and Thamnolia. These genera are currently placed in the order Lecanorales, apparently based solely on the character of lichenization since apothecia and other lichen reproductive structures are absent. Using the nucleotide characters of rDNA, we tested the phylogenetic position of these genera among the Ascomycota. Cladistic analyses of SSU nrDNA and partial LSU nrDNA did not support the recognition of the Siphulaceae. Rather, Siphula and Thamnolia represent independent origins of nonsexual lichens among the Icmadophilaceae; a family that is currently classified in the order Helotiales. In addition to these molecular characters, the secondary chemistry of these genera also supports their affinity with the Icmadophilaceae. We propose taxonomically emending the Icmadophilaceae to include the genera Siphula and Thamnolia. The phylogenetic relationships between the Icmadophilaceae and the Baeomycetaceae, the other family of lichenized fungi classified in the Helotiales, are discussed. Cladistic evidence is provided which demonstrates that the Baeomycetaceae is a distinct taxon from the Icmadophilaceae and the two families represent independent lichenization events. The phylogenetic relationships between these families and other higher taxa (e.g., families and orders) of the Ascomycota are also discussed.