This is a moss. Your photos show it in the dry state, with the leaves curled up. With a bit of moisture the leaves would uncurl, open out and become green. One or more species of Tortula are common on the trunks of rough-barked trees in numerous Canberra suburbs. Quite often a Tortula colony extends for well over a metre on a trunk but, when dry, is easily overlooked. If you look at the open leaves with a hand lens (or with the help of a macro lens on a camera) you will often see what looks like a scattering of lots of small green granules (as shown here http://www.cpbr.gov.au/bryophyte/photos-captions/tortula-papillosa-172.html). Each granule is an asexual propagule (technically called a gemma) and is capable of growing into a new plant. Gemma-bearing colonies are quite common in Canberra.
It was actually only noticed on the photo of the Lichens after looked at on the computer. As you mention it is easy to overlook and we did this. Thank you very much for the extra information, most interesting. It really is amazing what is all around us that we so easily just walk past without noticing. Thanks.