Following the abolishment of dual nomenclature, Stilbospora is recognised as having priority over Prosthecium. The type species of Stilbospora, S. macrosperma, is the correct name for P. ellipsosporum, the type species of Prosthecium. The closely related genus Stegonsporium is maintained as distinct from Stilbospora based on molecular phylogeny, morphology and host range. Stilbospora longicornuta and S. orientalis are described as new species from Carpinus betulus and C. orientalis, respectively. They differ from the closely related Stilbospora macrosperma, which also occurs on Carpinus, by longer, tapering gelatinous ascospore appendages and by distinct LSU, ITS rDNA, rpb2 and tef1 sequences. The asexual morphs of Stilbospora macrosperma, S. longicornuta and S. orientalis are morphologically indistinguishable; the connection to their sexual morphs is demonstrated by morphology and DNA sequences of single spore cultures derived from both ascospores and conidia. Both morphs of the three Stilbospora species on Carpinus are described and illustrated. Other species previously recognised in Prosthecium, speciﬁcally P. acerophilum, P. galeatum and P. opalus, are determined to belong to and are formally transferred to Stegonsporium. Isolates previously recognised as Stegonsporium pyriforme (syn. Prosthecium pyriforme) are determined to consist of three phylogenetically distinct lineages by rpb2 and tef1 sequence data, two of which are described as new species (S. protopyriforme, S. pseudopyriforme). Stegonsporium pyriforme is lectotypiﬁed and this species and Stilbospora macrosperma are epitypiﬁed. Based on DNA sequence data, the North American Stegonsporium acerophilum is recorded from Europe for the ﬁrst time, and new hosts from Acer sect. Acer are reported for S. opalus and S. pyriforme. Stilbospora and Stegonsporium are classiﬁed within the revived family Stilbosporaceae. Prosthecium appendiculatum, P. auctum and P. innesii are shown to be unrelated to the Stilbosporaceae and are recognised in three distinct genera, Phaeodiaporthe appendiculata, Alnecium auctum n. gen. and Calosporella innesii within Diaporthaceae, Gnomoniaceae and Sydowiellaceae, respectively. The generic types of these three monotypic genera are briefly described, illustrated and lecto- and epitypﬁed.