Arthopyrenia A. Massal., Ric. auton. lich. crost. (Verona): 165 (1852).
Non-lichenized on bark in terrestrial, temperate forest habitats. Thallus reduced and immersed in the substrate, whitish or indistinct, often forming dark brown hyphae over the substrate. Sexual morph: Ascomata scattered, prominent, brown-black, hemisphaerical, carbonaceous, ostiolate, ostiole round. Involucrellum not distinctly separated from excipulum, dark brown to carbonized, K+ sordid-green in section. Excipulum dense, proso- to paraplectenchymatous in thin sections, brown. Hamathecium comprising 0.5–0.7μm wide, densely packed paraphysoids connected to both the base and the top of the centrum, hyaline, straight to irregularly bent, branched and anastomosing. Asci forming in locules between the paraphysids, 8-spored, bitunicate, fissitunicate, broadly clavate, short-pedicellate, with rather broad, non-amyloid ocular chamber. Ascospores irregularly arranged to bi-seriate, oblong with the proximal end slightly tapering, hyaline, (1–)3- septate, with thin eusepta and rectangular lumina, smooth walled, not or very slightly constricted at the septa, the upper cells often slightly larger than the lower cells. Asexual morph: Pycnidia erumpent to prominent, visible as brown-black dots. Conidia acrogenous, either macro- or microconidia; macroconidia non-septate, bacillar, hyaline; microconidia non-septate, acicular, hyaline. Chemistry: Unidentified. perithecial wall pigment reacting K+ green (Adapted from Hyde et al. 2013).
Type species: Arthopyrenia cerasi (Schrad.) A. Massal.
Notes: Arthopyrenia is morphologically characterised by densely arranged paraphysoids developing from both the top and base of the centrum, and the K+ sordid-green perithecial wall (Foucard 1992; Harris 1995; Smith et al. 2009). Wijayawardene et al. (2017a) reported both the asexual morph and sexual morph of Arthopyrenia. Zahlbruckner (1921, 1926) defined Arthopyrenia as an assemblage of lichenized and non-lichenized ascomycetes with perithecioid ascomata and bitunicate asci. Harris (1995) provided a re-arrangement of Arthopyrenia and transferred the non-lichen forming species having short-celled paraphyses with refractive bodies near the septa, obpyriform asci with a distinctive apical region lacking a nasse and short rod-shaped microconidium in a new family Naetrocymbaceae. Aptroot (1998, 2002) disagreed with the treatment of Harris (1995) and suggested that Arthopyrenia should be considered in the original wide concept i.e. characterised by branched pseudoparaphyses, which may vanish, and sole-shaped ascospores. Still, Eriksson et al. (2003) accepted the taxa proposed by Harris (1995). Arthopyrenia is taxonomically accommodated in Arthopyreniaceae. Molecular markers available for Arthopyrenia include ITS, LSU, SSU, BTUB, RPB2, TEF-1 and mtSSU.