A crustose lichen, that is with its lower surface growing down into the rock. Thallus or lichen body forming a thin layer on the rock surface, light to dark brown, cracking into pieces like a jigsaw puzzle, with black showing between the pieces. Each large puzzle piece contains one or two fruiting bodies, called perithecia, hidden within it. These perithecia are shaped like squat bottles, but only the tops are visible as charcoal-colored depressions (right). Perithecia produce the reproductive spores. The spores (lower right) are visible only under a microscope. They are large for a lichen (a micrometer or µm is 1/1000 mm), transparent, and made of multiple cells.

Forms brown patches on limestone rock (lower left). Common in the Park, especially on the east slope.

The cracking brown thallus with black cracks and dark depressions are good identifiers. Close relatives are also possible in the Park, but microscopic examination of spores would be needed to be certain of their identity. This species is unusual compared to its relatives in having transparent rather than brown spores.

Note the black lumps visible on top of the lichen in the picture top left. These are parasites, Opegrapha pulvinata, that invade the lichen and suck up nutrients. Many of the rock jigsaws in the Park are infected with it.