Botanists Ken Hill and Lawrie Johnson were the first to define the genus "Corymbia" in 1995, identifying the bloodwoods, ghost gums and spotted gums as a group distinct from "Eucalyptus". Since 1995, there have been ongoing investigations into the relationships between the genera. Genetic analysis of ETS and ITS sequences of DNA in 2006 by Carlos Parra-O and colleagues of 67 taxa (47 of which were within "Corymbia") yielded "Corymbia" and "Angophora" as each other's closest relatives, with the genus "Eucalyptus" as an earlier offshoot. The small genera "Eucalyptopsis", "Stockwellia" and "Allosyncarpia" formed a clade which arose earlier still. In 2009, Parra-O and colleagues added more taxa and published a combined analysis of nuclear rDNA (ETS + ITS) and morphological characters published to clarify relationships within the genus. This confirmed two main clades, which they defined as the subgenera "Corymbia" and "Blakella". Species of "Corymbia" occur in all mainland states of Australia and in the Northern Territory. There are about 100 species, all endemic to Australia except for four species that also occur in New Guinea, and one that is endemic to that country.