| Summary: | Asexual reproduction, polyploidy and hybridization are well-known sources of taxonomic complexity in angiosperms. All these processes are believed to occur in Potentilla sect. Niveae (Rosaceae). Although it has been assumed that hybridization is common in section Niveae, this hypothesis has not been tested and recent studies suggest that phenotypic plasticity may sometimes better explain morphological intermediates in nature. To clarify the role of hybridization in the evolution of section Niveae, we tested two hybridization hypotheses for its eastern American Arctic species. The first is a potential hybrid between Potentilla nivea and Potentilla arenosa, and the second between Potentilla arenosa and Potentilla vahliana sensu lato. Twenty-four quantitative and 12 qualitative morphological characters were scored on specimens sampled from a representative range of the parental species and putative hybrids in the American Arctic east of the 100th meridian. Multivariate analyses showed that these two classes of characters give a congruent signal and that species form separate groups. Morphological evidence appears to give support to the hybridization hypothesis both between Potentilla arenosa and Potentilla nivea and between Potentilla arenosa and Potentilla vahliana sensu lato, although other explanations may also be conceivable. We discuss potential implications for the taxonomy of Potentilla and the study of hybridization in apomictic groups.
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