Heiomasia is a new genus that includes two sterile species producing unique isidia-like structures for vegetative dispersal. Their systematic position was clarified using molecular analysis of the small subunit of the mitochondrial ribosomal DNA (mtSSU). The two species form a strongly supported clade occupying a somewhat isolated position within Graphidaceae s.lat. The new genus is based on H. sipmanii (Aptroot, Lücking & Rivas Plata) Nelsen, Lücking & Rivas Plata comb. nov., a species from Southeast Asia with disc-shaped isidia-like structures, originally described in the genus Herpothallon. The second species, H. seaveyorum Nelsen & Lücking spec. nov., is known only from Florida; it produces robust, sausage-shaped isidia-like structures.