Prosthemium Kunze, Mykologische Hefte (Leipzig) 1: 17 (1817).
Saprobic in terrestrial habitats. Sexual morph: Ascomata solitary, scattered, or in small groups, immersed, erumpent or depressed globose, medium to large, black, ostiolate. Ostiole papillate, opening via a minute slit or a small conical swelling in the bark, ostiolar canal illed with a tissue of hyaline small cells. Peridium 1–2 layered comprised of compressed cells of textura angularis, apex comprises comparatively larger cells than the base. Hamathecium of dense, cellular, filiform, broad, septate pseudoparaphyses, embedded in a gelatinous matrix. Asci 8-spored, bitunicate, fissitunicate, ellipsoid, broadly cylindrical to broadly cylindro-clavate, with a short, narrow, thick pedicel, rounded at the apex with a minute ocular chamber. Ascospores biseriate, partially overlapping, narrowly oblong with broadly to narrowly rounded ends, brown to golden brown, muriform, 5–8 transverse septa and 1–2 vertical septa in some cells, constricted at each septum, smooth to verrucose wall with a mucilaginous sheath. Asexual morph: Pycnidia globose to subglobose, brown to black. Conidiophores unbranched, hyaline, septate. Macroconidia brown, staurosporous, with two main arms and 2 or 3 smaller arms. Main arms 4–5 transversely septate, with terminal cell hyaline to pale brown. Smaller arms continuous or 1–3 septate, hyaline to pale brown. Microconidia brown to dark brown, sometimes with 1–2 guttules, globose to ellipsoid, aseptate, thick-walled, smooth (Adapted from Yuan et al., 2020).
Type species: Prosthemium betulinum Kunze
Notes: Prosthemium was introduced by Kunze (1817) with Prosthemium betulinum as the type species. Prosthemium is characterized by solitary, scattered ascomata, fissitunicate, ellipsoid, broadly cylindrical to broadly cylindro-clavate asci and brown to golden brown, muriform ascospores. The asexual morph is coelomycetous characterized by staurosporous brown macroconidia and ellipsoid guttulate microconidia. Tanaka et al. (2010) provided molecular phylogeny of Prosthemium based on SSU, ITS and b-tubulin sequences. Prosthemium is considered as the asexual morph of Pleomassaria (Hantula et al., 1998; Hyde et al., 2013; Wijayawardene et al., 2014a). Ariyawansa et al. (2016) described Prosthemium sinense from China using morphology and phylogenetic analysis of ITS, LSU and TUB sequence data. Pem et al. in Yuan et al. (2020) described the sexual and asexual morph of P. betulinum as a new record from Italy. Prosthemium is morphologically and phylogenetically a distinct genus in Pleomassariaceae. Molecular markers available for Prosthemium include LSU, SSU, ITS and b-tubulin sequences.