Abstract
The order Meliolales comprises the families Armatellaceae and Meliolaceae. These are black mildews that grow on the surface of host plants, often regarded as minor plant pathogens. In this study, types or specimens of 17 genera of Armatellaceae and Meliolaceae were borrowed from herbaria and re-examined. Armatella is accepted in Armatellaceae and Amazonia, Appendiculella, Asteridiella, Cryptomeliola, Endomeliola, Irenopsis and Meliola are accepted in the family Meliolaceae. Laeviomeliola is synonymized under Meliola. Ceratospermopsis, Ectendomeliola, Haraea, Hypasteridium, Leptascospora, Metasteridium, Ophiociliomyces, Ophioirenina, Ophiomeliola, Parasteridium, Pauahia, Pleomeliola, Pleomerium, Prataprajella, Ticomyces, Urupe and Xenostigme are excluded from Meliolaceae, and are treated as doubtful genera or placed in ascomycetes genera incertae sedis. The type species of each genus is re-described and illustrated with photomicrographs. Notes are provided and comparisons made. Two new species of Meliola and one new species of Irenopsis are also introduced with molecular data and we provide the most populated phylogenetic tree of Meliolomycetidae to date. Meliola thailandicum was found on Dimocarpus longan (Sapindales) and Acacia auriculiformis (Fabales) and confirmed to be the same species in the molecular analyses. This has important implications as the several hundred Meliola species are recognized based on host associations. Thus the same species being recorded from two unrelated hosts sheds doubt on Meliola species being host-specific.