A flattened, leaf-like (foliose) lichen, a couple of inches across or less, divided into long narrow lobes, several millimeters long and a fraction of a millimeter across. Color is a dull brown. Undersurface is black centrally, white towards the edges, without any root-like structures to anchor it. Many tiny bowl-shaped structures with a brown rim and a black interior occur on top. These are apothecia wihich produce the reproductive spores (ascospores).
Grows on tree bark, especially along rivers -- the one pictured was found on the white poplar along Connelly's Run. May be common in the Park, but it is hard to find as it is so well camouflaged.
Resembles the shadow lichens (Phaeophyscia--see smooth shadow and bloody shadow), but lichens in that genus have a thick layer of black root-like structures (rhizines) beneath. This species, lacking these "roots" is thus called a "shadow crust."
The picture below center shows a cross-section of an apothecium of smooth shadow crust seen through a microscope. The dark structures near the top of the apothecium are bags (asci) of ascospores. Below right shows a single ascus containing 8 ascospores. (The scale bars are labeled in micrometers -- 1 µm is 1/1000 of a millimeter.)