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(American Journal of Botany. 2008;95:1122-1135.)
doi: 10.3732/ajb.0700008
© 2008 Botanical Society of America, Inc.
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Systematics and Phytogeography

Incongruence between cpDNA and nrITS trees indicates extensive hybridization within Eupersicaria (Polygonaceae)1

Sang-Tae Kim2 and Michael J. Donoghue

Department of Ecology and Evolutionary Biology, Yale University, P.O. Box 208106, New Haven, Connecticut 06520-8106 USA

ABSTRACT

Interspecific hybridization followed by polyploidization appears to have played a major role in plant diversification, but quantifying the contribution of this mechanism to diversification within taxonomically complex clades remains difficult. Incongruence among gene trees can provide critical insights, especially when combined with data on chromosome numbers, morphology, and geography. To further test our previous hypothesis on hybrid speciation in Persicaria (Polygonaceae), we performed molecular phylogenetic studies using three cpDNA regions and nuclear ITS sequences, with an emphasis on sampling within section Eupersicaria. Our analyses revealed major conflicts between the combined cpDNA tree and the nrITS tree; a variety of incongruence tests rejected stochastic error as the cause of incongruence in most cases. On the basis of our tree incongruence results and information on chromosome numbers, we hypothesize that the origin of 10 polyploid species involved interspecific hybridization. Our studies also support the recognition of several previously named species that have been treated as belonging within other species. Repeated allotetraploidy (as distinct from radiation at the tetraploid level) now appears to be the key mechanism governing the diversification of this taxonomically challenging group.

Key Words: allopolyploidy • cpDNA • Eupersicaria • hybridization • incongruence test • ITS • Persicaria • Polygonaceae • Polygonum

Received for publication 23 December 2007. Accepted for publication 4 June 2008.

FOOTNOTES

1 The authors thank members of the Donoghue laboratory at Yale and S. Sultan of Wesleyan University for valuable comments and discussion, and C.-L. Ma, M. Deng, and M.-H. Kim for great help during fieldwork in China and Korea. They are indebted to GH, NHA, and YU for critical specimens and especially to N. Ritter for his collections and information on South American species. This work was partially supported by a John F. Enders Fellowship from Yale University.

2 Corresponding author (e-mail: sang-tae.kim{at}tuebingen.mpg.de); current address: Max Planck Institute for Developmental Biology, Department of Molecular Biology, Spemannstrasse 37-39, 72070, Tuebingen, Germany






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