Aspicilia phaea

Aspicilia phaea (dusky sunken disk lichen) is a grayish brown to tan areolate crustose lichen commonly found on rock in coastal to inland parts of central and southern California. Described as new to science in 2007, it is endemic to (only found in) California. It grows on exposed or partially shaded siliceous rock, with a few known occurrences on serpentine rock. In rare cases full areolas do not form, and it appears as being cracked (rimose). There are often grayish or whitish spots on the areolas. The thallus is 2–8 cm in diameter, and 0.1– 1.2 mm thick. The areolas are irregularly sized and angular, giving the lichen body (thallus) the appearance of a mosaic of small polygons. A rim of dark tissue (prothallus) may surround the edges of the lichen. The fruiting body parts (apothecia) are flat to concave (especially in the thallus center), and slightly immersed in the thallus, appearing as sunken round to polygonal discs, often with a grey or white rim of thalline tissue. Lichen spot......read more on Wikipedia.