So close yet so far: the disjunct global range of Orthotrichum consobrinum (Orthotrichaceae) includes North America

Abstract. Intercontinental disjunct distributions of many bryophytes continue to raise questions about their nature and origin. While mounting evidence points to long-distance dispersal as a mechanism to explain broad distribution ranges, there is a need to clarify whether the disjunct populations belong to the same species connected by gene flow or actually harbor hidden genetic variation indicating speciation due to geographic isolation. During recent fieldwork, new populations of a moss morphologically matching Orthotrichum consobrinum were discovered in eastern North America. This moss had until this point been considered to be restricted to Eurasia. To shed light on the identity of these new populations and their nature as a species with intercontinental range versus cryptic speciation, we compared morphological characters with molecular sequence divergence over the global range of O. consobrinum and the putative American populations. Our results identify the North American specimens as belonging to O. consobrinum, forming a monophyletic group with specimens from eastern and western Asia. This study therefore provides an addition to the North American flora, alongside a description and images of distinguishing morphological features to facilitate the differentiation from the closely related Orthotrichum stellatum. The known distribution of O. consobrinum is now conceived as disjunct pan-Holarctic, adding new evidence to the long-distance dispersal capacities of bryophytes.