Anisomeridium (Müll. Arg.) M. Choisy, Icon Lich Univ 1: 24 (1928).
≡ Arthopyrenia sect. Anisomeridium Müll. Arg., Flora 66: 290 (1883).
Index Fungorum number: IF 201; Facesoffungi number: FoF 08073, 60 morphological species (Species Fungorum 2022), 4 species with molecular data.
Lichenized on bark or more rarely on leaves or rocks, possibly lichenicolous; in lowland to montane tropical to subtropical habitats, with few species extending into temperate regions. Sexual morph: Thallus usually ecorticate or sometimes with thin cortex, white or shades of grey-green to green. Photobiont Trentepohlia. Ascomata scattered or rarely clustered, erumpent to sessile, mostly black, carbonaceous, ostiolate, ostiole apical or lateral. Involucrellum present or reduced, carbonized. Excipulum dense, consisting of compressed hyphae, appearing prosoplectenchymatous in thin, bleached sections, hyaline to brown or brown-black. Hamathecium comprising paraphyses, hyaline, straight, branched and anastomosing. Asci (2–)8-spored, bitunicate, fissitunicate, cylindrical, short pedicellate, with narrow, nonamyloid ocular chamber and fuorescent cap- or ring-structures. Ascospores uni- or biseriate to irregularly arranged, ellipsoid-oval to broadly fusiform, small to medium-sized, hyaline to very rarely brown, 1(–3)-septate, with thin eusepta and rectangular lumina, smooth-walled or granular ornamented, sometimes slightly constricted at the septa, in 1-septate ascospores the upper cell often distinctly larger than the lower cell (very rarely the opposite). Asexual morph: Pycnidia common, immersed to sessile, visible as black dots but sometimes conspicuous and flask-shaped. Conidia acrogenous, either macro- or microconidia; macroconidia usually aseptate, (globose to) broadly ellipsoid to bacillar, hyaline, often forming clusters embedded in a gelatinous matrix, these clusters in some species in the form of sacci or cirri; microconidia aseptate, globose to broadly ellipsoid or fusiform, small, hyaline. Chemistry: Most species do not contain secondary substances; lichexanthone present in some taxa (Adapted from Hyde et al. 2013).
Type species: Arthopyrenia xylogena Müll. Arg.
Notes: Anisomeridium is characterised by ecorticate thallus, scattered or rarely clustered, erumpent to sessile ascomata, prosoplectenchymatous excipulum, hyaline, straight, branched and anastomosing hamathecium, cylindrical, short pedicellate asci, with narrow, nonamyloid ocular chamber and fluorescent cap- or ring-structures and hyaline to very rarely brown, 1(–3)-septate ascospores. Anisomeridium is the largest genus within Monoblastiaceae but is heterogeneous. Members of Anisomeridium are easily confused with species of Mycomicrothelia based on the brown ascospores (Lücking et al. 2011). Müller (1883) included only Arthopyrenia xylogena in Arthopyrenia sect. Anisomeridium, hence the terms ‘holo-’ and ‘lectotype’ cannot be formally applied to names above species according to ICN Art. 10.1, Note 1. Riedl (1963) and Harris (1995) considered Arthopyrenia xylogena as the lectotype of Anisomeridium. The asexual taxa Sarcinulella banksiae and Compsosporiella deightonii have been reported to be the pycnidial forms of Anisomeridium species and share similar morphological similarities and discharge of conidial masses in mucilage (Sutton and Alcorn 1983; Harris 1995; Aptroot 1999; Aptroot and Sipman 2001). Anisomeridium polypori was reported to have lichenicolous pycnidia found on dead Sticta weigelii in Guatemala which was interpreted as a lichenicolous fungus but it is not clear whether this species is saprobic or parasitizing the Sticta mycobiont, linked with its own photobiont or related with the photobiont from the host lichen (Etayo and Van den Boom 2006). Etayo (2002) reported Anisomeridium on a decaying Megalospora tuberculosa thallus in the Pyrenees. Lücking et al. (2017) accepted 200 species in Anisomeridium, but currently only 60 species are listed as several have been transferred to other genera (Hongsanan et al. 2020b). Anisomeridium is morphologically and phylogenetically a distinct genus in Monoblastiaceae. Molecular markers available for Anisomeridium include ITS, SSU, LSU, TEF-1 and RPB2.