Astrothelium Eschw., Syst. Lich.: 18, 26 (1824).
MycoBank number: MB 443; Index Fungorum number: IF 443; Facesoffungi number: FoF 08788; Over 250 morphologically defined 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, chiefly lowland to lower montane tropical habitats. Thallus distinctly corticate, yellow-brown to mostly green. Photobiont Trentepohlia. 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 0.5–0.7 µm wide 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. 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 superficial on various parts of the thallus.
Type species: Astrothelium conicum Eschw., Syst. Lich.:26 (1824) [= Astrothelium cinnamomeum (Eschw.) Müll. Arg., Flora 67: 670 (1884)].
Notes: Astrothelium traditionally included species with thallus-dominated perithecia featuring lateral, fused ostioles and transversely septate, astrothelioid ascospores. In its modern circumscription (Aptroot and Lücking 2016), practically all species with thickly corticate thalli, thallus-dominated perithecia, and astrothelioid ascospores are now included in this genus, regardless of the disposition of the perithecia and their ostioles or ascospore septation, with a total of over 250 taxa (Aptroot and Lücking 2016; Cáceres and Aptroot 2017; Aptroot and Weerakoon 2018; Aptroot et al. 2019). Astrothelium is essentially a fusion of the previously separated genera Astrothelium, Bathelium p.p., Campylothelium, Cryptothelium, Laurera, and Trypethelium p.p. Harris (1995) had already predicted the existence of this clade, suggesting the use of the name Laurera. However, Laurera postdates Astrothelium, a name Harris (1995) intended to reserve for a small group of species that have been shown to form part of a single, large clade including most species of the family (Lücking et al. 2016).