Geographic, climatic, and chemical differentiation in the Hypogymnia imshaugii species complex (Lecanoromycetes, Parmeliaceae) in North America

Abstract Hypogymnia imshaugii is one of the most common, conspicuous and morphologically variable epiphytic lichens of the Pacific coastal states and provinces. The species varies greatly in morphology and chemistry, suggesting multiple closely related species or one or more phenotypically plastic species. We sought to determine whether additional ecologically meaningful species might be present within the H. imshaugii complex. Improving our species concepts could potentially improve ecological inferences based on community sampling. Three relatively well-defined genetic groups and one residual group in the H. imshaugii complex were detected with haplotype networks based on the ITS locus; however, phylogenetic reconstructions on combined ITS, mtSSU, GPD1 and TEF1 loci did not reflect this pattern. At present, we have insufficient evidence to support defining any of these groups as new taxa. The four major chemotypes in H. imshaugii differed in frequency among the genetic groups. None of the genetic groups was, however, qualitatively uniform in chemotype. Only one chemotype occurred in a single genetic group, but several chemotypes occurred in that group. While broadly sympatric, each chemotype had a distinct geographic distribution, and each chemotype showed its own relationship to climate, as shown by regression of occurrences of chemotypes against climatic variables. The genetic variation detected within H. imshaugii did not correspond to geographic variation in morphology, chemistry, or climate. Within the broader H. imshaugii complex, we recommend treating H. amplexa as a synonym of H. imshaugii unless it can be more distinctly separated from the clinal variation in morphology, chemistry, or DNA sequences. In contrast to H. amplexa, however, H. inactiva and H. gracilis are both easily separated morphologically from H. imshaugii and do not intergrade with it.