Systematics of Corymbia

Project summary

The genus Corymbia was erected in 1995 by Ken Hill and Lawrie Johnson (Royal Botanic Gardens Sydney) to encompass 113 species of eucalypts. Bloodwood, the common name for Corymbia, refers to the propensity of the trees to exude a red, blood-like sap.

Eucalypts are one of the most important Australian plant groups, ecologically and economically, so there has been significant interest and debate over changing the names of more than a hundred species. Corymbia also includes very well-known horticultural subjects, such as the Lemon-scented Gum (Corymbia citriodora) and the Red-flowering Gum (Corymbia ficifolia).

Our collaborative project aimed to use both molecular and morphological characters to resolve the phylogeny of Corymbia because, despite great progress over the past decade, the monophyly of Corymbia was still questionable. Previous studies had only included a handful of the more than 100 species of Corymbia, whereas in this study sampling would include all the major subgroups: red bloodwoods, yellow bloodwoods, spotted gums and paper-fruit bloodwoods (or ghost gums).

Using nuclear ribosomal DNA (ITS and ETS) sequences and morphological characters we showed that genus Corymbia is monophyletic and related to Angophora, supporting the taxonomic treatment of the bloodwoods as a separate genus. Patterns of distribution and relationship are consistent with a deep divergence between species in eastern and south-western Australia, arguably before the mid-Miocene. Furthermore, our DNA studies revealed ITS pseudogenes in eucalypts, contributing to methodological issues involved with phylogenetic analysis of multicopy regions of DNA.

Detailed analysis within Corymbia has allowed us to provide a revised infrageneric classification, with the two major clades recognised as subgenera Corymbia and Blakella, and other groups as sections.

Summary of classification of Corymbia

Subgenus Corymbia (includes the red bloodwoods)

  • Section Corymbia – monotypic, only including C. gummifera
  • Section Septentrionales – red bloodwoods, excluding C. calophyllaC. ficifoliaC. gummifera and C. haematoxylon
  • Section Calophyllae – includes the three red bloodwoods endemic to south-west Western Australia, C. calophyllaC. ficifolia and C. haematoxylon

Subgenus Blakella (includes the ghost gums, spotted gums and yellow bloodwoods)

  • Section Abbreviatae – ghost gums or paper-fruited bloodwoods
  • Section Maculatae – spotted gums
  • Section Torellianae – monotypic, only including C. torelliana
  • Section Naviculares – yellow bloodwoods

This research is ongoing and funded by the Hermon Slade Foundation. New molecular tools, including next generation sequencing methods, will help us to answer controversial questions about the diversification of eucalypts and further refine their classification.

Project team

  • Frank Udovicic (Royal Botanic Gardens Melbourne)
  • Tanja Schuster (Royal Botanic Gardens Melbourne) (2013–)
  • Pauline Ladiges (School of Botany, The University of Melbourne)
  • Andrew Drinnan (School of Botany, The University of Melbourne)
  • Ken Hill (Royal Botanic Gardens Sydney) (2004-2008)
  • Michael Bayly (School of Botany, The University of Melbourne
  • Carlos Parra Osario (National University of Colombia, Bogota, Colombia) (2005-2009)

Support

  • Australian Research Council Linkage Project LP0455375
  • Hermon Slade Foundation
  • Maud Gibson Trust
  • Royal Botanic Gardens Melbourne
  • Royal Botanic Gardens Sydney
  • The University of Melbourne

Publications

Bayly, M.J., Rigault, P., Spokevicius, A., Ladiges, P.Y., Ades, P.K., Anderson, C., Bossinger, G., Merchant, A., Udovicic, F., Woodrow, I. and Tibbits, J. (2013).  Chloroplast genome analysis of Australian eucalypts – Eucalyptus, Corymbia, Angophora, Allosyncarpia and Stockwellia (Myrtaceae). Molecular Phylogenetics and Evolution 69, 704–716.

Ladiges, P., Parra-O., C., Gibbs, A., Udovicic, F.,  Nelson, G. and Bayly, M. (2011). Historical biogeographical patterns in continental Australia: congruence among areas of endemism of two major clades of eucalypts. Cladistics 27, 29-41.

Parra-O., C., Bayly, M., Drinnan, A.N., Udovicic, F. and Ladiges, P.Y. (2009). Phylogeny, major clades and infrageneric classification of Corymbia (Myrtaceae), based on nuclear ribosomal DNA and morphology. Australian Systematic Botany 22, 384–399.

Bayly, M.J., Udovicic, F., Gibbs, A.K., Parra-O., C. and Ladiges, P.Y. (2008). Ribosomal DNA pseudogenes are widespread in the eucalypt group (Myrtaceae): implications for phylogenetic analysis. Cladistics 24, 131–146.

Parra-O., C., Bayly, M., Udovicic, F. and Ladiges, P.Y. (2006). ETS sequences support the monophyly of the eucalypt genus Corymbia (Myrtaceae). Taxon 55, 653–663.

Ladiges, P.Y. and Udovicic, F. (2005). Comment on molecular dating of the age of eucalypts. Australian Systematic Botany 18, 291–293.