Evolution of non-lichenized, saprotrophic species of Arthonia (Ascomycota, Arthoniales) and resurrection of Naevia, with notes on Mycoporum

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. Arthoniaceae is a prime example including non-lichenized, saprotrophic lineages which potentially were precursors to lichenized taxa. In this study, we focused on saprotrophic species of Arthonia sensu lato, including new sequence data for Arthonia pinastri. We obtained fresh material of this taxon from a living branch of Fraxinus ornus in Italy to assess its taxonomic status and to elucidate its phylogenetic relationships within Arthonia. Thin sections of the thallus and ascomata of A. pinastri confirmed the absence of a photobiont. Maximum likelihood and Bayesian analyses of combined mtSSU, nuLSU and RPB2 sequence data placed the species close to A. dispersa (barely lichenized or non-lichenized) and A. punctiformis (non-lichenized) in a clade closely related to Arthonia sensu stricto, and the A. pinastri clade is here resurrected under the name Naevia. Ancestral character state analysis within a broader context of Arthoniales does not support the saprotrophic lifestyle to be a plesiomorphic feature, but suggests loss of lichenization in Naevia, as well as loss and possible regain in a second clade containing saprotrophic species and including taxa resembling Mycoporum, underlining the evolutionary plasticity of Arthoniales. These two clades constitute model taxa to further investigate the evolution of alternative biological lifestyles within the context of chiefly lichenized taxa.