Xanthopyreniaceae Zahlbr., in Engler & Prantl, Nat. Pflanzenfam., Edn 2 (Leipzig) 8: 91 (1926).

MycoBank number: MB 81525; Index Fungorum number: IF 81525; Facesoffungi number: FoF 07653, 53 species.

Lichen-forming fungi, lichenicolous or forming loose associations with cyanobacteria. Vegetative hyphae usually hyaline. Sexual morph: Ascomata perithecioid, solitary or in groups, superficial or immersed in the substrarum, subglobose. Peridium thin to thick, composed by elongated to roundish, more or less compresed cells of textura angularis. Involucrelum present in some species, with textura intricata. Hamathecium comprising thin, septate, highly branched and anastomosed interascal filaments. Asci 4–8-spored, thick-walled, bitunicate, fissitunicate, ovate to clavate, apedicellate, with a distinct ocular chamber. Ascopores irregularly arranged within the ascus, ellipsoid to broadly ellipsoid, hyaline, 1-septate, wall cell smooth, usually with a gelatinous shell. Asexual morph: Coelomycetous. Pycnidium, superficial or immersed in the substratum, black, with a small ostiole. Pycnidial wall thick-walled cells of textura angularis, composed of ± isodiametric or elongated cells. Conidiogenous cells ± cylindrical, phialidic. Conidiospores bacilliform to ellipsoid.

Type: Xanthopyrenia Bachm.

Notes: Xanthopyreniaceae was introduced by Zahlbruckner to accommodate the single species Xanthopyrenia tichothecioides (= Arthopyrenia tichothecioides), a species growing on periodically inundated calcareous rocks. The species was later combined into Pyrenocollema (P. tichothecioides) and subsequently many species associated with cyanobacteria, and with perithecioid ascomata, highly branched and anastomosed interascal filaments and hyaline 1-septate ascospores were transferred or described in Pyrenocollema (e.g. Santesson 1992; Coppins et al. 1992; McCarthy and Kantvilas 1999; Nordin 2002). However, Grube and Ryan (2002) stated that the type species of the genus, P. tremelloides is in fact a parasite on Nostoc and is not congeneric with X. tichothecioides, suggesting that the correct generic name for those species should be Collemopsidium, and many species of Pyrenocollema were subsequently combined into this genus (Grube and Ryan 2002; Mohr et al. 2004). Pérez-Ortega et al. (2016) studied the phylogenetic relationships of Xanthopyreniaceae using six molecular markers. Although they found Xanthopyreniaceae belongs to Dothiodeomycetes, and described the new order Collemopsidiales, their exact position remained elusive despite of using different taxa sampling, very likely due to the use of Arthoniomycetes as outgroup. Subsequent work by Liu et al. (2017) found high support for the sister relationships of Collemopsidiales with Monoblastiales. Based on uncertainties by Pérez-Ortega et al. (2016), Tedersoo et al. (2018) described the new class Collemopsidiomycetes which should be considered as a synonym of Dothiodeomycetes. Lumbsch and Huhndorf (2007) included the genera Collemopsidium, Didymellopsis, Frigidopyrenia, Pyrenocollema, and Zwackhiomyces as members of the Xanthopyreniaceae. Later, Wijayawardene et al. (2018) excluded Frigidopyrenia and Pyrenocollema from the family and placed them in Pezizomycotina genera incertae sedis. Unfortunately, no molecular data is available for Didymellopsis, Frigidopyrenia and Pyrenocollema. Pérez-Ortega et al. (2016) discussed that the number of species in the family may have been highly underestimated.