Molecular phylogeny suggests synonymy of Thelotremataceae within Graphidaceae (Ascomycota: Ostropales)

Family concepts in lichen-forming fungi are poorly understood and were traditionally based on easily observable characters. An example is the family Thelotremataceae, a species-rich group of crustose, predominantly tropical lichens with over 1,000 described species. Its distinction from Graphidaceae is largely based on ascoma shape (round vs. lirelliform). Previous studies already indicated that the distinction of these families is doubtful. However, these studies only included a few taxa of Thelotremataceae. Hence we obtained 96 new partial sequences of nuclear and mitochondrial ribosomal DNA, mostly of Thelotremataceae. We performed maximum parsimony and Bayesian phylogenetic analyses of a combined dataset of 105 samples, representing 97 species. Our results indicate that Graphidaceae and Thelotremataceac cannot be separated, but form several lineages within one strongly supported monophyletic lineage. Monophyly of Graphidaceae and Thelotremataceae each in their present circumscription was rejected significantly using two independent alternative topology tests. Consequently, Thelotremataceae is reduced to synonymy with Graphidaceae. Further, numerous genera in Graphidaceae and Thelotremataceae were found to be para- or polyphyletic, including all genera currently placed in Thelotremataceae, with the sole exception of Diploschistes. In Graphidaceae, Graphis and Sarcogropha are polyphyletic as currently circumscribed. However, since the topology within Graphidaceae s.l. largely lacks support and given the large number of species not yet studied, a thorough evaluation of the generic concept requires a larger dataset, including additional genes and taxa.