@Steve818 not a canker. This is the fully-developed, sporing state of one of the 'flat' fungi (or, to use the technical term, corticioid fungi). Xylodon australis is common on dead wood but at times you find quite large expanses on live trunks. The pinkish-brown to orange-brown colour and the surface with its short, densely-packed teeth tend to make this a fairly distinctive species. You find a few other genera of corticioid fungi on live trunks and in general it's a microscope job to get to genus.