Amplistroma is described as a new genus for A. carolinianum, A. diminutisporum, A. guianense, A. hallingii, A. ravum, A. tartareum and A. xylarioides. Species of Amplistroma are distinguished by large stromata of textura intricata with polystichous ascomata and long necks that are either erumpent from the stromatal surface or form bumps or protuberances. The type collection of Ceratostoma sphaerospermum was examined and found to be synonymous with Wallrothiella congregata. The distribution of W. congregata is expanded by collections from Costa Rica, the eastern United States and Puerto Rico. Wallrothiella congregata has ascomata that are long-necked and develop individually or are gregarious on the substrate but do not form large stromata. Amplistroma and Wallrothiella are distinguished by small asci with eight, minute, globose ascospores. An acrodontium-like anamorph occurs in both genera. Phylogenetic analyses of 28S large-subunit rDNA sequences group these taxa in a well supported clade distinct from known orders within the Sordariomycetidae but showing unsupported relationships with the Chaetosphaeriales and the Magnaporthaceae. Family Amplistromataceae is described for this clade and placed within the Sordariomycetidae incertae sedis.