| Summary: | Orthotrichum lyellii, O. papillosum, and O. pylaisii are reported new to Arizona based on specimens collected in Yavapai County. Orthotrichum lyellii is confirmed for Nevada from three counties along the California border. Orthotrichum papillosum also is confirmed from Nevada from one location near Lake Tahoe. Whether or not O. lyellii (sterile plants with brood-bodies) and O. papillosum (usually fertile plants without brood-bodies) are distinct taxa has been long debated. The occurrence in these out-lying localities in Nevada, where sterile, female plants of O. lyellii are found and fertile plants of O. papillosum occur in different localities, and in Arizona where both taxa occur adds weigh to their distinctiveness. Orthotrichum pylaisii is an uncommon, but widespread arctic-montane species. The Arizona specimen demonstrates a number of clear differences when compared to O. laevigatum and O. rupestre. Whether these western Cordilleran populations should be recognized as distinct from arctic ones in currently unclear.
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