A foliose lichen, that is, flat with an upper and lower surface, up to several inches across. Tightly attached to bark, or sometimes rock. The perimeter has small, branching lobes (right). Color is bluish gray, varying to greenish when wet. Lobes smooth and somewhat shiny, with tiny ridges and white spots (pseudocyphellae) visible under a hand lens. Towards the center it becomes darker and matte. A hand lens shows this is because of hundreds of tiny finger-like projections called isidia (lower left), which can break off and grow into new lichens. Higher magnification (30x at lower right) shows that each of the isidia is tipped with black.

Common in the eastern US. Somewhat sensitive to air pollution so likely to be more common deeper in the Park.

Look for the two-tone appearance, smooth at edges and darker, rougher in center. A hand lens can show the pseudocyphellae and isidia.