Or Parmotrema perforatum (a type of Shield lichen) Foliose lichen, gray-green, growing on trees (corticolous), with lobe margins bearing hair-like projections (cilia). The lobes rise up from the bark.
From the Guide to Common Lichens available for download as a PDF.
Around here, it grows on sickly sweet gum trees. That's a sweet gum branch that fell off during a little storm. I've found three different lichens growing on sickly sweet gum trees and no, they don't make the trees sick. They include common shield lichen, bristly beard lichen and the one you see above.
I'm glad to find your page - we definitely have similar interests. I love this shot with all its details on the lichen. They are fascinating pieces of nature.
