This little fungus specializes on this one species of bracket fungus.
Air pollution extirpated this whole genus of lichens from Pennsylvania about a hundred years ago. So why it was growing in Frick Park, in the middle of Pittsburgh, the air pollution capitol of the east, I do not know.
It was growing on an ash tree, attached to the trunk where the trunk was about 3 inches wide. The lichen clump is about 4 inches wide, with the longest branch about 4 inches long. The tree was infested with emerald ash borer, and had been recently cut down.
This may be an isolated waif, or it may be part of a larger population. I still have to do a better search of the immediate area, and of other ash trees around the park, to see if there are any other colonies.
The elastic cord inside each stem clearly identifies this as an Usnea. There are 9 species of this genus historically known from Pennsylvania; I haven't yet figured out which species this is or if any other Usneas have been collected in recent decades.