Rhagadodidymellopsis Fern. -Brime, Gaya, Llimona & Nav.-Ros., in Fernández-Brime et al., Plant and Fungal Systematics 65: 177 (2020).
Index Fungorum number: IF 835454; Facesoffungi number: FoF 09130, 1 morphological species (Species Fungorum 2022), no molecular data available.
Lichenicolous, growing superficially on the thallus of Endocarpon. Sexual morph: Ascomata black, perithecioid, unilocular, solitary or usually clustered inside a stromatic structure, with a clearly rugose and irregular surface, ascomal wall pseudoparenchymatous, blackish brown. Interascal filaments abundant, branched and anastomosing. Ostiolar filaments visible. Asci 8-spored, fissitunicate, thickened at apex, with distinct ocular chamber, clavate, stipitate. Ascospores hyaline, narrowly obovate to elongate ellipsoid, with smooth surface and conspicuous gelatinous sheath, uniseptate, markedly constricted at septum, heteropolar, with oil droplets. Asexual morph: unknown (adapted from Fernández-Brime et al. 2020).
Type species: Rhagadodidymellopsis endocarpi Fern. -Brime, Gaya, Llimona & Nav.-Ros.
Notes: Rhagadodidymellopsis is characterised by black, perithecioid, unilocular, solitary ascomata, clavate, stipitate asci and narrowly obovate to elongate ellipsoid ascospores. The stromatic ascomal wall of Rhagadodidymellopsis is similar to Rhagadostoma and the ascospores resemble those of Didymellopsis. Rhagadodidymellopsis differs from Didymellopsis and Zwackhiomyces in having grouped ascomata in the stromata, varied thickness of ascomatal wall around the grouped pseudothecia which form a markedly rugose excipular surface while in the latter two genera, ascomata are produced solitarily and peridium thickness is uniform and sometimes somewhat thicker towards the ostiole. Rhagadodidymellopsis endocarpi differs from D. perigena in that the latter has solitary, non-stromatic perithecioid ascomata, longer ascospores and occur on squamule margins of Placidium squamulosum (Khodosovtsev and Klymenko 2015; Fernández-Brime et al. 2020). Grube and Hafellner (1990) reported that D. perigena can grow on both Placidium and Endocarpon based on the specimen from France mentioned by Vouaux (1913). Vouaux (1913) also mentioned that the ascomata of D. perigena grow in the margin of the lichen squamules which resembles the growth of R. endocarpi. Fernández-Brime et al. (2020) could not observe Vouaux’s specimen and could not check if D. perigena as described by Vouaux (1913) belongs to R. endocarpi or to D. perigena. Fernández-Brime et al. (2020) revised D. perigena from Turkey found on Endocarpon cf. pusillum which matches the description of D. perigena. van den Boom (2012) also mentioned a specimen of D. perigena from Cabo Verde growing on E. pusillum but no morphological information or illustration of the fungus is available. Rhagadodidymellopsis endocarpi is unique in its ecology in that the surface of the stromata is always inhabited by cyanobacteria while this is not the case for other lichenicolous fungi. Rhagadodidymellopsis is morphologically and phylogenetically a distinct genus in Xanthopyreniaceae. Molecular data is lacking. Sequence data is needed to confirm this generic placement and the relationship of Rhagadodidymellopsis with other similar genera such as Didymellopsis.