Rhizocarpon quinonum McCune, Timdal & Bendiksby is described as a new species from two sites in Katmai National Park, south-western Alaska, in a suboceanic climate near the limit of trees on the Alaska Peninsula. Most similar in external appearance to R. arctogenum, R. bolanderi, R. leptolepis, and R. rittokense, the species is distinguished by the presence of an anthraquinone as a major substance. Mature apothecia are unknown, but ITS sequences are most similar to those of R. copelandii and R. jemtlandicum, although those species differ greatly in morphology from R. quinonum.
