A new mangrove fungus collected in Tioman Island, Malaysia, is morphologically similar to marine species of Saccardoella. It also phylogenetically groups with Saccardoella rhizophorae in the Dothideomycetes, based on combined analysis of partial SSU, LSU rRNA and TEF1 gene sequences. The new fungus and S. rhizophorae form a well-supported clade with Acrospermum spp. in the Acrospermaceae. Both species therefore do not belong in Saccardoella, a genus with unitunicate asci. A new genus, Dyfrolomyces, is established to accommodate the new fungus (Dyfrolomyces tiomanensis) while the three marine Saccardoella species (S. mangrovei, S. marinospora, S. rhizophorae) are transferred to the new genus. Dyfrolomyces is characterized by forming a clypeus on substrates, with immersed perithecial ascomata, bitunicate/fissitunicate asci and multi-septate ascospores with/without a sheath. Since D. rhizophorae and D. tiomanensis do not cluster with any known families in the Dothideomycetes, a new family, Dyfrolomycetaceae, is introduced to accommodate the Dyfrolomyces species.