Dearnessia Bubák, Hedwigia 58: 25 (1916).
Index Fungorum number: IF 7932; Facesoffungi number: FoF 07271, 1 morphological species (Species Fungorum 2021), molecular data unavailable.
Pathogenic on host. Asexual morph: Mycelium hyaline to brown, branched, septate. Conidiomata pycnidial, amphigenous, separate, globose, immersed, brown; wall of thin-walled textura angularis. Ostiole central, circular, papillate. Setae ostiolar, approximately straight, unbranched, tapered towards apex, dark brown, smooth, thin-walled, septate. Conidiogenous cells holoblastic, determinate, discrete, doliiform to ampulliform, hyaline, smooth and formed from the inner layer of the pycnidial wall. Conidia cylindrical to irregular, hyaline, 1–multi-transversely euseptate, rarely with 1–2 longitudinal eusepta, continuous or constricted, often tapered at the apex, base truncate, thin-walled, smooth, guttulate or not. Sexual morph: Unknown (Sutton 1980).
Type species: Dearnessia apocyni Bubák
Notes: Dearnessia was introduced by Bubák (1916) with D. apocyni as type species. Dearnessia is characterized by globose, immersed, brown conidiomata, ostiolar setae, doliiform to ampulliform conidiogenous cells, cylindrical to irregular hyaline conidia. Dearnessia has septoria-like morphology. Quaedvlieg et al. (2013) restudied the holotype specimen of D. apocyni but the latter was in poor condition. Fresh collection of this taxon is needed to establish the correct taxonomic position. Dearnessia is currently treated as a doubtful genus in Mycosphaerellaceae.