Pseudodidymellaceae fam. nov.: Phylogenetic affiliations of mycopappus-like genera in Dothideomycetes

Abstract

The familial placement of four genera, Mycodidymella, Petrakia, Pseudodidymella, and Xenostigmina, was taxonomically revised based on morphological observations and phylogenetic analyses of nuclear rDNA SSU, LSU, tef1, and rpb2 sequences. ITS sequences were also provided as barcode markers. A total of 130 sequences were newly obtained from 28 isolates which are phylogenetically related to Melanommataceae (Pleosporales, Dothideomycetes) and its relatives. Phylogenetic analyses and morphological observation of sexual and asexual morphs led to the conclusion that Melanommataceae should be restricted to its type genus Melanomma, which is characterised by ascomata composed of a well-developed, carbonaceous peridium, and an aposphaeria-like coelomycetous asexual morph. Although Mycodidymella, Petrakia, Pseudodidymella, and Xenostigmina are phylogenetically related to Melanommataceae, these genera are characterised by epiphyllous, lenticular ascomata with well-developed basal stroma in their sexual morphs, and mycopappus-like propagules in their asexual morphs, which are clearly different from those of Melanomma. Pseudodidymellaceae is proposed to accommodate these four genera. Although Mycodidymella and Xenostigmina have been considered synonyms of Petrakia based on sexual morphology, we show that they are distinct genera. Based on morphological observations, these genera in Pseudodidymellaceae are easily distinguished by their synasexual morphs: sigmoid, multi-septate, thin-walled, hyaline conidia (Mycodidymella); globose to ovoid, dictyosporus, thick-walled, brown conidia with cellular appendages (Petrakia); and clavate with a short rostrum, dictyosporus, thick-walled, brown conidia (Xenostigmina). A synasexual morph of Pseudodidymella was not observed. Although Alpinaria was treated as member of Melanommataceae in a previous study, it has hyaline cells at the base of ascomata and pseudopycnidial, confluent conidiomata which is atypical features in Melanommataceae, and is treated as incertae sedis.