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(American Journal of Botany. 2008;95:756-765.) doi: 10.3732/ajb.0800049 © 2008 Botanical Society of America, Inc.

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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

Received for publication 11 February 2008. Accepted for publication 7 April 2008.

FOOTNOTES

¹ This journal paper of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 1018, was supported by Hatch Act and State of Iowa funds and was made possible by grant number P01ES012020 from the National Institute of Environmental Health Sciences (NIEHS) and the Office of Dietary Supplements (ODS), NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS, NIH. Mention of commercial brand names does not constitute an endorsement of any product by the U. S. Department of Agriculture or cooperating agencies. J.-A. McCoy and other members of the Center for Research on Botanical Dietary Supplements at Iowa State University were helpful in providing feedback and comments throughout the research. L. Urbatsch kindly provided DNA samples for sequence analysis.

⁷ Author for correspondence (e-mail: jfw{at}iastate.edu)

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