Microthyriaceae Sacc., Syll. fung. (Abellini) 2: 658 (1883).

MycoBank number: MB 81008; Index Fungorum number: IF 81008; Facesoffungi number: FoF 06747, 120 species.

Saprobic on leaves. Hyphae mostly absent, superficial, brown, septate, branched, reticulate. Sexual morph: Thyriothecia superficial, circular, flattened, dark brown, solitary or gregarious, with a round, central ostiole, with poorly developed basal plate. Upper wall brown, comprising radially arranged cells of textura prismatica, often darkened at the ostiole and tapering at the margin. Hamathecium comprising asci inclined from the base and rim towards the central ostiole. Pseudoparaphyses present or absent. Asci 8-spored, bitunicate, fissitunicate, cylindrical to obpyriform, with or without a pedicel, with or without an ocular chamber at the tip. Ascospores overlapping uni- to 3-seriate, fusiform to ellipsoidal, hyaline or brown, usually 1-septate, with cilia or appendages, smooth-walled. Asexual morph: Mycelium consisting of hyaline to pale brown, smooth to verruculose, branched, septate hyphae. Conidiophores micronematous or macronematous, mononematous, arising from a brown stroma or from superficial hyphae, erect, solitary, unbranched or branched, straight or flexuous, smooth or roughened, septate, subcylindrical, pale brown to brown; microconidiophores when present, reduced to conidiogenous cells on hyphae, visible as slight thickenings on hyphal cells, somewhat erumpent, pale brown, truncate apex. Conidiogenous cells mono- to polyblastic, integrated, terminal, smooth or verruculose, determinate or sympodial, clavate, subcylindrical, ampulliform or ovoid. Ramoconidia when present, pale brown, verruculose, subcylindrical to fusoidellipsoid, aseptate, giving rise to branched chains of conidia. Conidia solitary or in branched chains, sometimes radial on compact heads, acrogenous or acropleurogenous, verruculose, subcylindrical to ellipsoid, obclavate, pale brown, aseptate to multi-septate, sometimes rostrate; hilum inconspicuous, truncate, sometimes unthickened, sometimes thickened; conidia in Hamatispora consisting of a main axis and lateral branches; main axis hook-shaped with a long tail bearing lateral branches; lateral branches straight,developing from different cells of the helicoid part of the main axis.

Type: Microthyrium Desm.

Notes: The phylogenetic placement of this family was first provided by Wu et al. (2011b), represented by Microthyrium microscopicum. New genera and new species in Microthyriaceae with molecular data were provided to support the placement of Microthyriaceae. Eleven genera are accepted in this family based on morphology and phylogeny.

The genera Condylospora, Spirosphaera and Stomiopeltis are not included in the family due to their polyphyletic characters or lack of evidence. Caribaeomyces is excluded from the family as it is typical of Asterinales by its hyphopodia and structure of upper walls. Hansfordiella and Isthmospora are also excluded from the family, as they are asexual morphs of Trichothyrium (Trichothyriaceae) (Wijayawardene et al. 2017a). Monorhizina was referred as a member of Microthyriaceae in some studies. This genus was synonymised under Lauterbachiella and Rhagadolobium by Dingley (1972) and Müller and von Arx (1962), respectively.