| Summary: | Umbilicaria semitensis was described by Tuckerman in 1872 based on a specimen from Yosemite National Park. Despite the species having muriform spores, in contrast to simple spores in U. angulata, U. semitensis has long been treated as a synonym of U. angulata, owing to the superficial similarities of the thallus. Analysis of the ITS and LSU regions of nrDNA supports the hypothesis that the species are distinct. In addition to the spore and DNA differences, the two species are largely allopatric, and only know to co-occur in one site in Oregon. Umbilicaria semitensis ranges from southern California to southern Oregon, while U. angulata ranges from California to arctic Alaska.
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