Recent molecular phylogenetic studies of the lichen family Acarosporaceae have shown that genera in this group, as traditionally defined, are not monophyletic and that changes are required to accommodate the discovery that taxa with disparate thallus morphologies are often closely related. Here we use phylogenetic inferences of mtSSU sequence data to show that seven species (Acarospora dispersa, A. rhizobola, A. terricola, Melanophloea americana, M. coreana, M. montana and Thelocarpella gordensis), currently placed in four genera and three families, and with divergent thallus morphologies, all belong to a single strongly supported clade within the Acarosporaceae. Members of the clade all have apothecia with an incurving parathecium which forms globose apothecia in which the apothecial disc is less than or equal to half the width of the equatorial diameter of the hymenium, and long bacilliform conidia. We transfer the species to Trimmatothelopsis, the oldest generic epithet available for the group and provide a taxonomic treatment that includes analysis of the published literature pertaining to these taxa, a key to species and descriptions of the four taxa that occur in North America. Rhizohyphal bundles are reported from two terricolous species, T. terricola and T. rhizobola.