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Phylogenetic, morphological, and chemotaxonomic incongruence in the North American endemic genus Echinacea¹

² Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, Iowa 50011 USA ³ USDA-ARS North Central Regional Plant Introduction Station, Ames, Iowa 50011 USA ⁴ Department of Genetics, University of Georgia, Athens, Georgia 30602 USA ⁵ Departamento de Biodiversidad y Conservación, Real Jardín Botánico, CSIC, Madrid 28014 Spain ⁶ School of Bioresource Science, Andong National University, Andong Gyeongbuk, 760-749 South Korea

ABSTRACT

The study of recently formed species is important because it can help us to better understand organismal divergence and the speciation process. However, these species often present difficult challenges in the field of molecular phylogenetics because the processes that drive molecular divergence can lag behind phenotypic divergence. In the current study we show that species of the recently diverged North American endemic genus of purple coneflower, Echinacea, have low levels of molecular divergence. Data from three nuclear loci and two plastid loci provide neither resolved topologies nor congruent hypotheses about species-level relationships. This lack of phylogenetic resolution is likely due to the combined effects of incomplete lineage sorting, hybridization, and backcrossing following secondary contact. The poor resolution provided by molecular markers contrasts previous studies that found well-resolved and taxonomically supported relationships from metabolic and morphological data. These results suggest that phenotypic canalization, resulting in identifiable morphological species, has occurred rapidly within Echinacea. Conversely, molecular signals have been distorted by gene flow and incomplete lineage sorting. Here we explore the impact of natural history on the genetic organization and phylogenetic relationships of Echinacea.

Key Words: Asteraceae • chloroplast DNA • Echinacea • incomplete lineage sorting • phylogenetics • single-copy nuclear DNA