By their fruit you will recognise them: species notes and typifications in Western Australian species of Opercularia (Rubiaceae: Anthosperminae)

An examination of herbarium collections, type material and reference to original species descriptions has found that several species names of Opercularia Gaertn. have been misapplied in Western Australia. This nomenclatural confusion stems from a combination of missing types, a lack of reference to either types or correctly identified specimens, and no recent revisions of the genus. Previously presumed to be extinct, O. acolytantha Diels is neotypified and discussed here as an extant species endemic to the Mallee and Esperance bioregions of Western Australia. Opercularia hirsuta Benth. is found to be a far rarer species than previously thought, with no material matching the type collected since the 1860s. Opercularia nubicola A.S.Markey is described as a new species with affinities to O. aspera Gaertn. Opercularia rubioides Juss. is reduced to synonymy with O. aspera,which is excluded from Western Australia. Opercularia scabrida Schltdl. is also excluded from Western Australia. This paper provides updated notes, illustrations and a key to Western Australian species of Opercularia. Characteristics of the infructescence, fruits and seed are diagnostic for these species and are illustrated here for this purpose.