Umbilicaria phaea is a brown, umblicate foliose lichen that grows up to 6 cm in diameter, sometimes in colonies covering large patches of desert rocks.:127 One variety that grows in northern California is brilliant red. It is (monophyllous) with a single 1 - 5 cm flattish leaf-like cap on top of an anchoring stem(umblicate). The leaflike top is smooth with some lobes, roughly circular, thin, and brittle. The lower surface is light gray to light brown.