Evolution of non-lichenized, saprotrophic species ofArthonia(Ascomycota,Arthoniales) and resurrection ofNaevia, with notes onMycoporum

Fungi that are barely lichenized or non-lichenized and closely related to lichenized taxa, the so-called borderline fungi, are an important element in reconstructing the evolutionary history of lichenized lineages.Arthoniaceaeis a prime example including non-lichenized, saprotrophic lineages which potentially were precursors to lichenized taxa. In this study, we focused on saprotrophic species ofArthoniasensu lato, including new sequence data forArthonia pinastri. We obtained fresh material of this taxon from a living branch ofFraxinus ornusin Italy to assess its taxonomic status and to elucidate its phylogenetic relationships withinArthonia. Thin sections of the thallus and ascomata ofA.pinastriconfirmed the absence of a photobiont. Maximum likelihood and Bayesian analyses of combined mtSSU, nuLSU and RPB2 sequence data placed the species close toA. dispersa(barely lichenized or non-lichenized) andA.punctiformis(non-lichenized) in a clade closely related toArthoniasensu stricto, and theA.pinastriclade is here resurrected under the nameNaevia. Ancestral character state analysis within a broader context ofArthonialesdoes not support the saprotrophic lifestyle to be a plesiomorphic feature, but suggests loss of lichenization inNaevia, as well as loss and possible regain in a second clade containing saprotrophic species and including taxa resemblingMycoporum, underlining the evolutionary plasticity ofArthoniales. These two clades constitute model taxa to further investigate the evolution of alternative biological lifestyles within the context of chiefly lichenized taxa.