Michael D. Crisp, Bui Q. Minh, Bokyung Choi, Robert D. Edwards, James Hereward, Carsten Kulheim, Yen Po Lin, Karen Meusemann, Andrew H. Thornhill, Alicia Toon, and Lyn G. Cook
Eucalypts (Myrtaceae tribe Eucalypteae) are currently placed in seven genera. Traditionally, Eucalyptus was defined by its operculum, but when phylogenies placed Angophora, with free sepals and petals, as sister to the operculate bloodwood eucalypts, the latter were segregated into a new genus, Corymbia. Yet, generic delimitation in the tribe Eucalypteae remains uncertain. Here, we address these problems using phylogenetic analysis with the largest molecular data set to date. We captured 101 low-copy nuclear exons from 392 samples representing 266 species. Our phylogenetic analysis used maximum likelihood (IQtree) and multispecies coalescent (Astral). At two nodes critical to generic delimitation, we tested alternative relationships among Arillastrum, Angophora, Eucalyptus, and Corymbia using Shimodaira's approximately unbiased test. Phylogenetic mapping was used to explore the evolution of perianth traits. Monophyly of Corymbia relative to Angophora was decisively rejected. All alternative relationships among the seven currently recognized Eucalypteae genera imply homoplasy in the evolutionary origins of the operculum. Inferred evolutionary transitions in perianth traits are congruent with divergences between major clades, except that the expression of separate sepals and petals in Angophora, which is nested within the operculate genus Corymbia, appears to be a reversal to the plesiomorphic perianth structure. Here, we formally raise Corymbia subg. Blakella to genus rank and make the relevant new combinations. We also define and name three sections within Blakella (Blakella sect. Blakella, Blakella sect. Naviculares, and Blakella sect. Maculatae), and two series within Blakella sect. Maculatae (Blakella ser. Maculatae and Blakella ser. Torellianae). Corymbia is reduced to the red bloodwoods.
Eucalypts are currently placed in three genera. Traditionally, Eucalyptus was defined by the operculate perianth. When earlier phylogenies placed Angophora, which has free sepals and petals, within Eucalyptus as sister to the bloodwood clade, which has opercula, the bloodwoods were segregated into a new genus, Corymbia. Here, we present a new next generation sequencing phylogeny of 392 species-level eucalypt taxa using 101 targeted low-copy nuclear loci. We find that Angophora is actually nested inside Corymbia and is sister to the red bloodwoods (Corymbia s.s.). A supported clade comprising the rest of Corymbia (spotted gums, yellow-jacket bloodwoods, and ghost gums) is thus separated from the red bloodwoods and requires a new generic name, which we here describe formally as Blakella. This phylogeny reveals homoplasy in the perianth evolution of the eucalypts. Either free petals were lost in the common ancestor of eucalypts and regained in Angophora, or opercula originated independently in the other eucalypt lineages.
