Calothyriopsis Höhn., Sber. Akad. Wiss. Wien, Math.- naturw. Kl., Abt. 1 128(7–8): 552 (1919).
Index Fungorum number: IF 761; Facesoffungi number: FoF 06750, 4 morphological species (Species Fungorum 2022), molecular data unavailable.
Biotrophic on the upper surface of leaves forming very small circular spots. Mycelium superficial, without lateral hyphopodia, but with irregular hyphopodia-like branches which penetrate the host epidermal cells. Sexual morph: Thyriothecia circular, scattered, superficial, membranaceous or a slightly carbonaceous, black to black-brown, basal peridium poorly developed, ostiole not clear, dissolving; in section lenticular. Upper wall consisting of loose irregularly arranged parallel cells from the central ostiole to the outer rim. Peridium of two strata, outer layer composed of black-brown pseudoparenchymatous cells of compact textura prismatica and inner layer composed of light-brown cells of textura angularis. Hamathecium of parallel arranged asci inclined towards the central ostiole and short branching pseudoparaphyses embedded in mucilage. Asci 8-spored, bitunicate, fissitunicate, obclavate, apedicellate and lacking a distinct ocular chamber, not bluing in IKI. Ascospores overlapping biseriate, oval, mostly rounded at the ends, hyaline, two-celled, the upper cell wider than lower cell, rough-walled. Asexual morph: Unknown (Adapted from Wu et al. 2011).
Type species: Calothyriopsis conferta (Theiss.) Höhn.
Notes: Calothyriopsis was introduced by Höhnel (1919) with C. conferta as type species. Calothyriopsis is characterized by circular, scattered, superficial thyriothecia, fissitunicate, obclavate, apedicellate asci, hyaline, two-celled ascospores. Several authors treated Calothyriopsis in Microthyriaceae (Müller and von Arx 1962; von Arx and Müller 1975; Lumbsch and Huhndorf 2010). Calothyriopsis resembles members of Microthyriaceae in having circular thyriothecia with superficial hypha, a central ostiole, obclavate asci and two-celled ascospores but differs in that the arrangement of the thyriothecial cells are nearly parallel compared to the neat arrangement in Microthyrium. Calothyriopsis also lacks an ostiole which makes its placement in Microthyriaceae questionable. Calothyriopsis is currently treated as a distinct genus in Microthyriaceae but fresh collections with DNA sequence data are needed to confirm the taxonomic placement of the genus. Calothyriopsis also needs epitypification.