A taxonomic monograph of the ascomycete genus (asexual dematiaceous hyphomycetes, sexual morphs unknown) is provided. Recent phylogenetic analyses demonstrated the polyphyly of this genus. The type species of pertains to the within , while other saprobic species clustered far away within , , and , whereas lichenicolous species belong to a monophyletic clade that represents the order , but for most species assigned to sequence data and phylogenetic analyses are not yet available. The main focus of the present taxonomic study was on a revision of the lichenicolous species. Since the currently available phylogenetic analyses do not allow final taxonomic conclusions at generic rank, the exclusion of lichenicolous species from . has been postponed pending a broader sampling and more phylogenetic data of allied ascomycete genera within the order . For the interim, ., including lichenicolous and saprobic species, is maintained. The taxonomic background, history, generic description and discrimination from morphologically confusable genera, phylogeny, biology, host range and distribution, and species concept of species are briefly outlined and discussed. Keys to the species of divided by ecological groups (lichenicolous taxa, saprobic taxa) are provided, supplemented by a tabular key to lichenicolous species based on host (lichen) families and genera. Twenty-nine lichenicolous species and a sp. (putative asexual morph of ) as well as 16 saprobic species are described in detail and illustrated by drawings, macroscopic photographs, light microscopic and SEM micrographs, including six new lichenicolous species ( on on on and on , on ), three new saprobic species ( on on on ), and one new combination, . Most saprobic species are wood-inhabiting (on bark, decorticated trunks and twigs, rotten wood), whereas lichenicolous species grow on thalli and fruiting bodies (mostly apothecia) of lichens, mostly without causing any evident damage, but they are nevertheless confined to their host lichens, or they are obviously pathogenic and cause either disease of the thalli (, and ) or at least thallus discolorations or necroses (, , , , , and ). and induce the formation of distinct galls. The range of micro-morphological traits for taxonomic purposes is limited in species, but size, shape and septation of conidiophores and conidia, including surface ornamentation, provided basic characters. Mycelium, stromata and arrangement of conidiophores are less important for the differentiation of species. Lichenicolous species are widespread on a wide range of lichens, with a focus in the northern hemisphere, mainly in northern temperate regions, including arctic-subartic habitats (18 species, , 62 % of the lichenicolous species). Eleven lichenicolous species, , , , , are also known from collections in non-temperate Asia, Australia and South America (38 % of the species). Most collections deposited in herbaria are from northern temperate to arctic-subarctic regions, which may reflect activities of lichenologists and mycologist dealing with lichenicolous fungi in general and in particular. Most lichenicolous species are confined to hosts of a single lichen genus or few closely allied genera (26 species, , 97 % of the lichenicolous species), but only three species, , , and , have wider hosts ranges. Excluded, doubtful and insufficiently known species assigned to are listed at the end, discussed, described and in some cases illustrated, including comb. nov. (≡ ), (≡ ), comb. nov. (≡ ), (≡ ), and (≡ ).