About Umbilicaria phaea Tuck.
Umbilicaria phaea is a brown, umbilicate foliose lichen that grows up to 6 cm (2.4 in) in diameter. It sometimes forms colonies that cover large patches of desert rocks. One variety growing in northern California is brilliant red. This lichen is monophyllous, with a single 1 – 5 cm flattish leaf-like cap that sits on top of an anchoring umbilicate stem. The leaf-like upper surface is smooth with some lobes, and is roughly circular, thin, and brittle. Its lower surface ranges from light gray to light brown. It bears up to 2.5 mm black circular to slightly polygonal fruiting bodies called apothecia, which are slightly sunken into the main non-fruiting thallus. It grows on siliceous boulders in very dry climates of western North and South America, where it is usually the most common member of its genus.
