Didymocyrtis Vain., Acta Soc. Fauna Flora fenn. 49(no. 2): 221 (1921).
Index Fungorum number: IF 1554; Facesoffungi number: FoF 08330, 25 morphological species (24 species as Didymocyrtis, 1 species as Diederichomyces; Species Fungorum, 2022), 14 species with molecular data.
Lichenicolous. Sexual morph: Ascomata (absent in some species) perithecioid (pseudothecia); ascomatal wall dark brown, pseudoparenchymatous, in longitudinal section comprising polyhedral, loosely flattened cells forming a textura angularis, pigmented in the hyphal cell walls. Hamathecial filaments paraphysoids, persistent, septate, with some branches and anastomoses. Asci fissitunicate, narrowly cylindrical, endoascus laterally thickened when young, apically thickened when mature, with a small ocular chamber, ascal wall I– and K/I– except dextrinoid reaction of ascal periplasma, hymenial ‘gel’ I– and and K/I–, 8-spored. Ascospores ± uniseriate to half-overlapping, pale brown to brown, usually pigmented from an early stage of development, relatively thin-walled, transversally 1–3-septate, upper part slightly broader than lower one, with rounded ends, most species with a distinct sculpture in light microscopy, a distinct perispore visible in young spores of some species in K. Asexual morph: Conidiomata (absent in some species) Phoma-like, with unilocular, ostiolate pycnidia; pycnidia generally undistinguishable from perithecia, except sometimes by the smaller size; pycnidial wall similar to perithecial wall. Conidiophores lacking. Conidiogenous cells attached to the conidiomal wall and lining the cavity, hyaline; conidiogenesis phialidic, not proliferating. Conidia hyaline, simple, smooth-walled, not embedded in a gelatinous matrix, usually with rounded ends (Adapted from Ertz et al., 2015).
Type species: Didymocyrtis consimilis Vain.
Notes: Didymocyrtis was introduced by Vain (1921) with D. consimilis as type species. Didymocyrtis is characterized by perithecioid ascomata, paraphysoids, persistent, septate hamathecial filaments, narrowly cylindrical asci and pale brown to brown pigmented ascospores. The asexual morph is characterized by Phoma-like conidiomata, phialidic conidiogenesis and hyaline, simple, smooth-walled conidia not embedded in a gelatinous matrix, generally with rounded ends. Vainio (1921) described Didymocyrtis with D. consimilis together with D. physciicola (Nyl.) Vain. (based on Mycoporum physciicola Nyl., a later heterotypic synonym of Sphaerellothecium parietinarium (Linds.) Hafellner & V. John) and Mycoporum epistygium Nyl. Vainio (1921) provided the combination Didymocyrtis epistygia. Ertz et al. (2015) resurrected Didymocyrtis based on phylogenetic analysis of LSU and ITS sequence data to accommodate lichenicolous Phoma-like taxa of the family Phaeosphaeriaceae and synonymized the genera Diederichia and Diederichomyces with Didymocyrtis. Ertz et al. (2015) also provided the new combinations Didymocyrtis bryonthae, D. cladoniicola, D. foliaceiphila, D. infestans, D. kaernefeltii, D. melanelixiae, D. pseudeverniae, D. ramalinae, D. slaptoniensis and D. xanthomendozae, introduced the new name D. epiphyscia for Phoma physciicola and provided an identification key to Didymocyrtis species. Didymocyrtis can be distinguished from Polycoccum s. str. based on the narrowly cylindrical asci, monostichously arranged ascospores, thin paraphysoids, thin-walled, medium (reddish)- brown ascospores and a Phoma-like asexual morph (Ertz et al., 2015). Didymocyrtis also differs from Polycoccum s. str. in that the latter causes galls formation on the host lichens while this does not occur with Didymocyrtis species. Didymocyrtis is currently a distinct genus in Phaeosphaeriaceae. Molecular markers available for Didymocyrtis include LSU, SSU, ITS, tub2, RPB2, TEF1.