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This first picture quite unusual, it grows more squarist than circular. I have checked this website (they are so similar, could not make up my mine which one is this one) http://www.rbgsyd.nsw.gov.au/science/Evo...
very sunny position on the Tibouchina tree branch.
Looks like Parmotrema perlatum but to be sure it would be necessary more detail and an image of the underside