During an ongoing study of marine fungi growing on Avicennia marina in the Red Sea coast of Saudi Arabia, a new coelomycete was collected in the genus Amarenographium. The new species is characterized by muriform, brown conidia with one polar gelatinous cap and sheath and holoblastic phialidic conidiogenesis. Amarenographium solium sp. nov. differs from the two known species of Amarenographium by the large size of its pycnidia, a thick (62–75 µm) two-layered peridial wall of the conidiomata that appears as textura epidermoidea in surface view and conidia with one apical appendage. Phylogenetic analysis of SSU and LSU rDNA sequences showed that the new species and thus genus Amarenographium grouped consistently with Medicopsis romeroi with high bootstrap support and form a basal clade to the families: Montagnulaceae and Trematosphaeriaceae, order Pleosporales, Dothideomycetes.