Unusual to see it on this plant. I usually only find them on one particular species of Eucalypt. Was there a Eucalyptus nearby? Perhaps it had fallen down.
Thanks for the ID, Alison Milton. Yes, it was on the edge of a eucalyptus grove - mostly E. cinerea, dives and macrorhyncha, and with some mannifera and haemastoma not too far away. I don't recognise the species of plant that it's on.