Molecular phylogenetic analyses of a multigene matrix of partial nuSSU-ITS-LSU rDNA, rpb2 and tef1 sequences were performed to investigate the phylogenetic relationships of Corynespora, Exosporium and Helminthosporium species. Based on phylogenetic analyses and morphology, the genus Exosporium is synonymised with Helminthosporium, and the genus Corynespora is revealed as polyphyletic. Corynespora smithii is confirmed to be closely related to the generic type C. cassiicola and its morphology is described and illustrated. Exosporium tiliae, Corynespora caespitosa, C. endiandrae, C. leucadendri and C. olivacea are recognised in Helminthosporium, and Splanchnonema quercicola and S. kalakadense are combined in Helminthosporium. Based on pure culture studies and DNA sequence data, Massaria heterospora and Massarinula italica are shown to be the sexual morphs of Helminthosporium tiliae and H. microsorum, respectively. European accessions of Splanchnonema quercicola are recognised to differ from the North American type and are described as Helminthosporium quercinum. The sexual morph of H. oligosporum is recorded and described for the first time. The generic type of Helminthosporium, H. velutinum, is epitypified with a recent collection from the type host, Fagus sylvatica. Based on sequence data, Helminthosporium genistae is recognised as a distinct species. Several species for which subperidermal stromata have been reported are shown to be fungicolous on Diaporthales, the “stromata” representing aborted and transformed host stromata or conidiomata: H. caespitosum, H. microsorum, H. quercicola and H. quercinum on Coryneum spp.; H. hispanicum on conidiomata of Juglanconis juglandina; H. juglandinum on conidiomata of Diaporthe sp.; H. oligosporum and H. tiliae on Hercospora tiliae. The newly described H. austriacum is fungicolous on Amphisphaeria cf. millepunctata (Xylariales).