Megaloseptoria Naumov, Bolêz. Rast. 14: 144 (1925).
Index Fungorum number: IF 8876; Facesoffungi number: FoF 08625, 1 morphological species (Species Fungorum 2022), no molecular data available.
Mycelium immersed, branched, septate, brown. Sexual morph: Unknown. Asexual morph: Conidiomata pycnidial, separate, globose, slightly papillate, dark brown to black, superficial, sessile, often aggregated in groups, unilocular, thick-walled; wall of several cell layers of brown textura angularis, more darkly pigmented on the outside. Ostiole single, circular. Conidiophores hyaline, branched, septate (mainly at the base), smooth, straight or irregular, formed from the inner cells of the pycnidial wall. Conidiogenous cells enteroblastic, determinate, discrete or integrated, doliiform, ampulliform or irregularly cylindrical, hyaline, smooth, collarette evident, channel wide, periclinal thickening present. Conidia hyaline to pale brown with several transverse eusepta, continuous, tapered near the obtuse apex and truncate base, thin-walled, smooth, cylindrical, straight or slightly curved, often with 2 guttules in each cell (adapted from Quaedvlieg et al. 2013; Videira et al. 2017).
Type species: Megaloseptoria mirabilis Naumov
Notes: Megaloseptoria is characterised by globose, slightly papillate, dark brown to black conidiomata, hyaline, branched, septate conidiophores, enteroblastic, determinate, discrete or integrated conidiogenous cells and hyaline to pale brown conidia with several transverse eusepta. Megaloseptoria differs from Septoria in having aggregated conidiomata in a black stroma, which does not occur in Septoria s. str. Quaedvlieg et al. (2013) re-examined the holotype specimen of M. mirabilis and provided an updated account of the genus. The placement of Megaloseptoria in Mycosphaerellaceae is doubtful.