Peridiothelia D. Hawksw., Bull. Br. Mus. Nat. Hist., Bot. 14(2): 120 (1985).
Saprobic on host. Sexual morph: Ascomata arising singly, scattered, colonies not delimited by a black line, erumpent, hemisphaerical, base applanata, lacking a distinct basal fringe, ostiole somewhat depressed to slightly papillate, black. Peridium dark reddish-brown, scarcely changed in potassium hydroxide, consisting of subglobose to polyhedral pseudoparenchymatous cells mainly, the outer layers of cells and their interstices becoming occluded with red-brown material and sometimes difficult to differentiate in section; basal tissue almost absent at first but at maturity poorly developed, continuous or interrupted, consisting of cells similar to the peridium in all respects; ascomatal cavity lined internally by 3−7 layers of hyaline compressed pseudoparenchymatous cells, centrum turning blue in iodine. Pseudoparaphyses cellular, persistent, numerous, septate, irregularly branched and anastomosing. Asci arising from the tissue lining the base of the ascomata, vertically orientated, elongate-clavate to subcylindrical, short-stalked, bitunicate with a distinct internal apical beak, 8-spored. Ascospores distichously arranged in the asci, ellipsoid, uniseptate, constricted at the septum, the cells equal in size or the lower slightly narrower, apices rounded, olive brown to reddish brown, slightly verruculose, with only a thin gelatinous sheath scarcely apparent when mature. Asexual morph: Unknown. Sometimes erumpent from bark with a superficial torulose dark brown mycelium which could possibly originate from ascospores but there is no strong evidence for this statement (adapted from Hawksworth 1985).
Type species: Peridiothelia fuliguncta (Norman) D. Hawksw.
Notes: Peridiothelia is characterised by single or scattered ascomata, dark reddish-brown peridium, septate, irregularly branched and anastomosing cellular pseudoparaphyses, and ellipsoid,uniseptate ascospores. The asexual morph is unknown. Members of Peridiothelia are differentiated based on ascospore size (Hawksworth 1985). Eriksson and Hawksworth (1991) placed Peridiothelia in Phaeosphaeriaceae. Barr (1992) transferred Peridiothelia to Pleomassariaceae and this treatment was followed by Wijayawardene et al. (2018). Peridiothelia is currently a distinct genus in Pleomassariaceae but molecular data is lacking. Fresh collections and DNA sequence data are needed to confirm the taxonomic placement of Peridiothelia.