Karstenula Speg., Decades Mycologicae Italicae 7–12: no. 94 (in sched.) (1879).
MycoBank number: MB 2549; Index Fungorum number: IF 2549; Facesoffungi number: FoF 00042; 22 morphological species (Species Fungorum 2020), 1 species with molecular data.
Type species – Karstenula rhodostoma (Alb. & Schwein.) Speg., Decades Mycologicae Italicae 7–12: no. 94 (1879).
≡ Sphaeria rhodostoma Alb. & Schwein., Consp. fung. (Leipzig): 43 (1805).
Notes – Karstenula is an ambiguous genus, due to its morphological similarities with different families (Zhang et al. 2012b, Ariyawansa et al. 2014d). For instance, Karstenula species share some similarities with Didymosphaeria in having ascomata seated in a subiculum or beneath a clypeal thickening and sometimes apical cells become reddish or orange-brown (Barr 1990a). The ascomata of Karstenula rhodostoma are similar to those found in Byssosphaeria and Herpotrichia, such as the paler area around the ostiole and even in peridium and development under a subiculum. However, based on multi-gene phylogenies Ariyawansa et al. (2014d) revealed that Karstenula is in Didymosphaeriaceae, but further collections are needed for resolve the ambiguity of this genus.