U.S.A., Colorado, Boulder, West base of Steamboat Mountain, foothills of Front Range 2 miles N. W. of Lyons.
1900 meters
1900 m.
On shelving horizontal surfaces of sandstone ledges.
Forms with pale greenish thalli are characteristic of alpine sites, while the rufous cortical color is developed in stable habitats at lower altitudes with high insolation. The development of a white edge to the thallus is variable in both habitats. Desert forms occurring exclusively on soil have a pale thallus which becomes heavily pruinose. There are no morphological characters of any value to consistently separate these forms. Deeply concave squamules with recurved margins are characteristic of the soil forms. Substrate: saxicolous.