Megalotremis Aptroot, Biblioth Lichenol 44: 124 (1991).
MycoBank number: MB 26295; Index Fungorum number: IF 26295; Facesoffungi number: FoF 08077; 16 morphologically defined species (this paper); molecular data available for one species.
Lichenized on bark, in tropical regions. Thallus usually with thin, cartilaginous cortex, rarely ecorticate, greenish grey to white. Photobiont Trentepohlia. Ascomata scattered, usually erumpent, black but at least partly covered by thalline layer, typically carbonaceous, ostiolate, ostiole apical or lateral. Involucrellum present, carbonized. Excipulum dense, consisting of compressed hyphae, appearing prosoplectenchymatous in thin, bleached sections, brown to brown-black. Hamathecium comprising 0.5–0.7 µm wide paraphyses, hyaline, straight, branched and anastomosing. Asci (1–)2–8-spored, bitunicate, fissitunicate, cylindrical, short pedicellate, with broad, non-amyloid ocular chamber and fluorescent cap-structures. Ascospores uni-seriate to irregularly arranged, ellipsoid-fusiform, rather large [50–130(–225) × (18–)20–45(–60) µm], sometimes with the upper cell enlarged, hyaline, 1-septate, with internal, needle- shaped crystals. Pycnidia rare. Conidia acrogenous, either macro- or microconidia; macroconidia usually aseptate, (globose to) ellipsoid, (4–)5–9(–15) × 2–5(–15) µm large, hyaline; microconidia aseptate, globose to broadly ellipsoid or fusiform, small, 2–7(–7) × 1.5–2(–4) µm large, hyaline; macro- and/or microconidia in some species aggregated into conglutinate masses sometimes deposited outside the pycnidia.
Chemistry: Secondary substances absent.
Type species: Megalotremis verrucosa (Makhija & Patw.) Aptroot, Biblioth. Lichenol. 44: 126 (1991).
Notes: In the protologue, Aptroot (1991) did not compare Megalotremis with Anisomeridium but placed the new genus in Trypetheliaceae because of the endospore thickenings; he also pointed out the ‘internal folds’ of the ascospores which were subsequently interpreted as crystals (Aptroot et al. 2008). Harris (1995) synonymized Megalotremis under Anisomeridium, stating that corticate thalli, one of the perceived differences, also occur in the latter genus. Harris (1995) further suspected that the second species of Megalotremis included in the protologue, M. biocellata, was related to Arthopyrenia sensu lato. Aptroot et al. (2008) differentiated Megalotremis from Anisomeridium by the corticate thallus and large ascospores with endospore thickenings, and from Trypetheliopsis (as Musaespora) by the absence of campylidioid asexual morphs.