Yes, the Corymbias are a new group (relatively) as has been stated, that were originally Eucalypt. So, for example, Eucalyptus maculata (spotted gum) became Corymbia Maculata.
Interestingly, the Angophoras (rough barked apple etc) were orginally Eucalypts too, but were declassified as Eucalypts quite a long time ago.
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