Xylariomycetidae (Ascomycota) is a highly diversified group with variable stromatic characters. Our research focused on inconspicuous stromatic xylarialean taxa from China, Italy, Russia, Thailand and the United Kingdom. Detailed morphological descriptions, illustrations and combined ITS-LSU-rpb2-tub2-tef1 phylogenies revealed 39 taxa from our collections belonging to Amphisphaeriales and Xylariales. A new family (Appendicosporaceae), five new genera (Magnostiolata, Melanostictus, Neoamphisphaeria, Nigropunctata and Paravamsapriya), 27 new species (Acrocordiella photiniicola, Allocryptovalsa sichuanensis, Amphisphaeria parvispora, Anthostomella lamiacearum, Apiospora guiyangensis, A. sichuanensis, Biscogniauxia magna, Eutypa camelliae, Helicogermslita clypeata, Hypocopra zeae, Magnostiolata mucida, Melanostictus longiostiolatus, M. thailandicus, Nemania longipedicellata, N. delonicis, N. paraphysata, N. thailandensis, Neoamphisphaeria hyalinospora, Neoanthostomella bambusicola, Nigropunctata bambusicola, N. nigrocircularis, N. thailandica, Occultitheca rosae, Paravamsapriya ostiolata, Peroneutypa leucaenae, Seiridium italicum and Vamsapriya mucosa) and seven new host/geographical records are introduced and reported. Divergence time estimates indicate that Delonicicolales diverged from Amphisphaeriales + Xylariales at 161 (123–197) MYA. Amphisphaeriales and Xylariales diverged 154 (117–190) MYA with a crown age of 127 (92–165) MYA and 147 (111–184) MYA, respectively. Appendicosporaceae (Amphisphaeriales) has a stem age of 89 (65–117) MYA. Ancestral character state reconstruction indicates that astromatic, clypeate ascomata with aseptate, hyaline ascospores that lack germ slits may probably be ancestral Xylariomycetidae having plant-fungal endophytic associations. The Amphisphaeriales remained mostly astromatic with common septate, hyaline ascospores. Stromatic variations may have developed mostly during the Cretaceous period. Brown ascospores are common in Xylariales, but they first appeared in Amphisphaeriaceae, Melogrammataceae and Sporocadaceae during the early Cretaceous. The ascospore germ slits appeared only in Xylariales during the Cretaceous after the divergence of Lopadostomataceae. Hyaline, filiform and apiospores may have appeared as separate lineages, providing the basis for Xylariaceae, which may have diverged independently. The future classification of polyphyletic xylarialean taxa will not be based on stromatic variations, but the type of ring, the colour of the ascospores, and the presence or absence or the type of germ slit.