Sunken Button Lichen

Buellia spuria (disc lichen) is a white to light ashy gray crustose areolate lichen that grows on rocks (epilithic) in montane habitats. It has a black edge from the conspicuous, more or less continuous prothallus, which can also be seen in the cracks between the areolas forming a hypothallus, and in sharp contrast with the whitish or ashy colored areolas. It prefers mafic (siliceous) rock substrates. In Joshua Tree National Park is can be seen on...