Petrakia Syd. & P. Syd., in Sydow & Sydow, Annls mycol. 11(5): 406 (1913).
Index Fungorum number: IF 9277; Facesoffungi number: FoF 01820, 6 morphological species (Species Fungorum 2022), 4 species with molecular data.
Saprobic or pathogenic on host. Sexual morph: Ascomata epiphyllous, partly immersed in leaf tissue, solitary or rarely confluent, globose-depressed, brown to black; apex with a central ostiolar perforation, without periphyses. Peridium pseudoparenchymatous. Hamathecium of hyaline septate pseudoparaphyses. Asci cylindrical, bitunicate, fissitunicate, containing 8 ascospores in biseriate arrangement. Ascospores fusoid, straight to curved, tapering towards the ends, hyaline to light brown, with one median to submedian primary euseptum, constricted at the primary septum, at maturity sometimes with additional transverse septa. Asexual morph on natural hosts is of two types (synanamorphs). (1) mycopappus-like and (2) petrakia-, xenostigmina- or blastostromalike. Conidiomata sporodochial, epiphyllous. Conidiophores macronematous, simple or branched, septate, sub cylindrical, short. Conidiogenous cells terminal, conidiogenesis holoblastic. Conidia solitary, hyaline or brown, multicellular, phragmo-, dictyo- or dictyostaurosporous, variously shaped from irregularly subglobose, fusoid, falcate to sigmoid (Adapted from Jaklitsch and Voglmayr 2017).
Type species: Petrakia echinata (Peglion) Syd. & P. Syd.
Notes: Petrakia was introduced by Sydow and Sydow (1913) with P. echinata as type species. Petrakia is characterized by epiphyllous, partly immersed ascomata, cylindrical, bitunicate, fissitunicate asci and fusoid, straight to curved ascospores. The asexual morph of Petrakia is of two types, firstly mycopappus-like and secondly, petrakia, xenostigmina- or blastostroma-like. Petrakia echinata was previously known as Epicoccum echinatum found on Acer pseudoplatanus but was not congeneric with the type species of Epicoccum, E. nigrum. Butin et al. (2013) described the teleomorph of P. echinata and gave an account of its complete life cycle. Jaklitsch and Voglmayr (2017) emended the generic concept of Petrakia and provided an updated description of both sexual and asexual morphs. Jaklitsch and Voglmayr (2017) transferred Mycodidymella and Xenostigmina to Petrakia based on morphology and phylogenetic analyses of LSU, SSU, ITS and TEF1. Hashimoto et al. (2017) did not accept the treatment of Jaklitsch and Voglmayr (2017). On the contrary, Beenken et al. (2020) agreed with Jaklitsch and Voglmayr (2017) based on phylogenetic evidence using LSU, ITS, RPB2 and TEF1 sequences from their study and suggested that Pseudodidymella should be accommodated within Petrakia. In the phylogenetic analysis of Beenken et al. (2020), Petrakia, including P. echinata and P. deviata is polyphyletic. The spermogonia of Petrakia is Phoma-like (Butin et al. 2013; Hashimoto et al. 2017; Jaklitsch and Voglmayr 2017). Petrakia resembles Mycodidymella, Petrakia and Pseudodidymella in having mycopappus-like synanamorphs of nearly same morphology which is unique to Melanommataceae. Petrakia is phylogenetically distinct from Mycopappus s. str. as the latter belongs to the Sclerotiniaceae (Helotiales) (Park et al. 2013; Beenken et al. 2020). Petrakia can be differentiated from similar genera such as Mycodidymella, Petrakia, Pseudodidymella and Xenostigmina in the presence and form of macroconidia however, Beenken et al. (2020) mentioned that the differences in macroconidia morphology and absence of macroconidia does not warrant splitting of Petrakia into several small genera. Members of Petrakia share similar ecological niches and life cycles (Beenken et al. 2020). The anamorph names Blastostroma and Pycnopleiospora are synonyms of Petrakia (Turland et al. 2018; Beenken et al. 2020). Petrakia is morphologically and phylogenetically a distinct genus in Melanommataceae (Phookamsak et al. 2014; Tian et al. 2015). Ideal molecular markers to introduce species of Petrakia include LSU, ITS, RPB2 and TEF1.