Cladistic Relationships and Biogeographic Patterns in the Peppermint Group of Eucalyptus (Informal Subseries Amygdalininae, Subgenus Monocalyptus) and the Description of a New Species, E. willisii

A preliminary study of eastern Monocalyptus suggested that the peppermint eucalypts, informal subseries Amygdalininae, form a monophyletic group whose sister taxon is series Pilulares. Subseries Amygdalininae was then analysed using four cladistic methods: transformed cladistic method, Wagner trees, a branch and bound method (all three being parsimony methods) and character compatibility analysis. The branch and bound method produced the shortest trees, four in all. They suggested that, within the Amygdalininae, Eucalyptus pulchella is the sister species to E. amygdalina, which in turn is the sister species to all other taxa. The remaining species from Tasmania form a monophyletic group characterized by, for example, protruding oil glands on seedling and juvenile-leaf margins. The Victorian taxa form a monophyletic group characterized by high oil gland densities and lack of anthocyanin pigment on the lamina of juvenile leaves at node 7. Tasmanian and mainland forms attributed to E. nitida were treated as separate terminal taxa and it was shown that they are not sister taxa. Tasmanian populations are typical E. nitida Hook. f. and a new species, E. willisii, is here erected for the mainland populations. A revised classification of subseries Amygdalininae and a formal description of E. willisii sp. nov. are appended. A vicariance-biogeographic analysis is also included.