Architrypethelium Aptroot, Biblioth. Lichenol. 44: 120 (1991).
MycoBank number: MB 26294; Index Fungorum number: IF 26294; Facesoffungi number: FoF 08787; eight morphologically defined species (Aptroot and Lücking 2016; Lücking et al. 2017; Luangsuphabool et al. 2018); molecular data available for four species (Lücking et al. 2016; Luangsuphabool et al. 2018).
Lichenized on bark in terrestrial, chiefly lowland to lower montane tropical habitats. Thallus distinctly corticate, yellow-brown to olive-green. Photobiont Trentepohlia. Ascomata solitary to aggregated, erumpent to prominent, brown-black but usually covered by thallus layer except for ostiolar area, coriaceous to carbonaceous, ostiolate, ostiole apical or lateral. Involucrellum reduced, brown-black. Excipulum prosoplectenchymatous, brownish to colorless. Hamathecium comprising 0.5–1 µm wide paraphysoids, hyaline, straight, branched and anastomosing, embedded in a gelatinous matrix, in some species inspersed with oil drop- lets. Asci 2–8-spored, bitunicate, fissitunicate, oblong-ellipsoid, short pedicellate, with a non-amyloid ocular chamber. Ascospores irregularly arranged, oblong-ellipsoid, hyaline to mostly dark brown, 3–5-septate and very large (usually over 100 µm) or rarely muriform and small, somewhat distoseptate but not astrothelioid, smooth-walled or with longitudinal wall folds or crystals, not or slightly constricted at the septa, surrounded by a mucilaginous sheath. Pycnidia unknown.
Chemistry: lichexanthone sometimes produced on thallus surface.
Type species: Architrypethelium seminudum (Mont.) Apt- root. [= Architrypethelium nitens (Fée) Aptroot in Aptroot et al., Biblioth. Lichenol. 97: 38 (2008)].
Notes: For discussion see Aptroot and Lücking (2016). The genus currently includes eight species. With the recent, surprising discovery of a species with rather small, muriform ascospores falling into this clade (Luangsuphabool et al. 2018), the generic boundaries towards Astrothelium have become more diffuse.