Formal recognition of Eucalyptus platydisca (Myrtaceae), an arid-zone monocalypt from south-western Australia

The new species Eucalyptus platydisca is formally described, the species having been long recognised as a distinct taxon under the manuscript name E. platydisca and under various phrase names including the common name Jimberlana mallee. The new species is known from just two populations near Norseman in Western Australia and is included in Western Australia’s Schedule of Declared Rare (Endangered) Flora. The new species is closely related to, but readily distinguishable from, E. diversifolia, differing in the narrower juvenile leaves, the consistently 7-flowered inflorescences, the longer, conical to horn-shaped operculum, the broader fruits with a consistently broad disc and the granite hill habitat. Eucalyptus platydisca is probably a relictual species and occurs in the lowest rainfall environment of any monocalypt (Eucalyptus subgenus Eucalyptus). The new species is part of E. subser. Neuropterae, and a key for the subseries is presented.