Identification: This rock-dwelling lichen is so
thin that it looks at first like rust on the rock. It appears most commonly on granite, but can
appear on other non-calcareous rocks. Its fruiting structures (apothecia) are
dark red and very small, less than a millimeter across, wide and flat, like irregular tiles,
without the white powdery covering that occurs in some other lichens. This is the only
rock-dwelling lichen with such a dark red appearance.