Astrothelium
Astrothelium Eschw., Syst. Lich.: 18, 26 (1824).
Index Fungorum number: IF 443; Facesoffungi number: FoF 08788, 245 morphological species (Aptroot and Lücking 2016; Lücking et al. 2017), molecular data available for over 50 species (Lücking et al. 2016).
Lichenized on bark in terrestrial, mainly lowland to lower montane tropical habitats. Thallus distinctly corticate, yellow-brown to mostly green. Photobiont Trentepohlia. Sexual morph: Ascomata scattered, clustered, aggregated in pseudostromata, or fused with common ostiole, immersed to sessile, brown-black but usually covered by thick thallus layer except for ostiolar area, globose to pear-shaped or conical, coriaceous to carbonaceous, ostiolate, ostiole round. Excipulum prosoplectenchymatous, dark brown to brown-black. Hamathecium comprising paraphysoids, hyaline, straight, branched and anastomosing, embedded in a thick, gelatinous matrix. Asci 1–8-spored, bitunicate, fissitunicate, obclavate, short pedicellate, with a non-amyloid ocular chamber. Ascospores irregularly arranged to uni- or biseriate, fusiform-ellipsoid to oblong-cylindrical, hyaline, septate to muriform, with distinct distosepta and sometimes eusepta and diamond-shaped lumina (best visible in septate ascospores), smooth-walled, not or slightly constricted at the septa, often surrounded by an evanescent mucilaginous material on the outside, either as polar pads, or irregular median pads or a complete sheath enveloping the whole ascospore. Asexual morph: Pycnidia known from a few species, immersed to erumpent, visible as black dots. Conidia acrogenous, rod shaped, hyaline. Chemistry: lichexanthone sometimes produced on thallus surface; yellow to orange or red anthraquinones and perylenequinones often produced in the medulla of the thalline layer covering the perithecia and sometimes in the thallus medulla or superfcial on various parts of the thallus (adapted from Hyde et al. 2013).
Type species: Astrothelium conicum Eschw.
Notes: Astrothelium is characterised by scattered, clustered ascomata, aggregated in pseudostromata, prosoplectenchymatous excipulum, fissitunicate, obclavate, short pedicellate asci and fusiform-ellipsoid to oblong-cylindrical, hyaline, septate to muriform ascospores. The asexual morph is characterised by immersed to erumpent conidiomata, visible as black dots and acrogenous, rod shaped, hyaline conidia. Astrothelium previously accommodated all species belonging to Trypetheliaceae with thallus-dominated perithecia having fused, lateral ostioles and transversely septate ascospores (Hyde et al. 2013). In its current concept, Astrothelium is the largest genus in Trypetheliaceae and shows much discrepancy in perithecial arrangement and ascospore septation. Astrothelium comprise species with both transversely septate and muriform ascospores together with apical, lateral, or fused ostioles which were earlier placed in other artificial genera such as Bathelium, Cryptothelium, Laurera, and Trypethelium. Cryptothelium and Laurera are now no longer used and are synonyms of Astrothelium. Harris (1995) suggested the use of the name Laurera which is older than Astrothelium but this has not been followed by subsequent authors. Astrothelium has a unique astrothelioid ascospore with thick distosepta which makes the lumina appear diamond-shaped (Sweetwood et al. 2012). The ascospores of Astrothelium are quite similar to the genera in Graphidaceae (Fissurinoideae) and Massariaceae but they are phylogenetically distant (Rivas Plata et al. 2012; Hyde et al. 2013). Astrothelium is morphologically and phylogenetically a distinct genus in Trypetheliaceae. Molecular markers available for Astrothelium include ITS, LSU, SSU, TEF-1, RPB1, RPB2 and mtSSU.
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