AOBPreview originally published online on January 30, 2009
Annals of Botany 2009 104(3):457-467; doi:10.1093/aob/mcp004
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This article appears in the following Annals of Botany issue: Special Issue: Orchid Biology [View the issue table of contents]
Molecular phylogenetics and the evolution of fruit and leaf morphology of Dichaea (Orchidaceae: Zygopetalinae)
1 Department of Botany, University of Florida, Gainesville, FL 32611-8526, USA
2 Florida Museum of Natural History, University of Florida, PO Box 117800, Gainesville, FL 32611-7800, USA
3 Jardín Botánico Lankester, Universidad de Costa Rica, Apartado 1031-7050 Cartago, Costa Rica
* For correspondence. E-mail kneubig{at}flmnh.ufl.edu
Received: 29 April 2008 Returned for revision: 8 July 2008 Accepted: 4 December 2008 Published electronically: 30 January 2009
Background and Aims: The orchid genus Dichaea, with over 100 species found throughout the neotropics, is easily recognized by distichous leaves on long stems without pseudobulbs and flowers with infrastigmatic ligules. The genus has previously been divided into four sections based primarily on presence of ovary bristles and a foliar abscission layer. The aim of this work is to use DNA sequence data to estimate phylogenetic relationships within Dichaea and map the distribution of major morphological characters that have been used to delimit subgenera/sections.
Methods: Sequence data for the nuclear ribosomal internal transcribed spacers and plastid matK, trnL intron, trnL-F spacer and ycf1 for 67 ingroup and seven outgroup operational taxonomic units were used to estimate phylogenetic relationships within Dichaea. Taxa from each of the four sections were sampled, with the greatest representation from section Dichaea, the most diverse and taxonomically puzzling group.
Key Results: Molecular data and morphology support monophyly of Dichaea. Results indicate that section Dichaeopsis is polyphyletic and based on symplesiomorphies, including deciduous leaves and smooth ovaries that are widespread in Zygopetalinae. There are at least three well-supported clades within section Dichaeopsis. Section Pseudodichaea is monophyletic and defined by setose ovaries and leaves with an abscission layer. Sections Dichaea and Dichaeastrum are monophyletic and defined by pendent habit and persistent leaves. Section Dichaeastrum, distinguished from section Dichaea primarily by a glabrous ovary, is potentially polyphyletic.
Conclusions: The leaf abscission layer was lost once, occurring only in the derived sections Dichaea and Dichaeastrum. The setose fruit is a more homoplasious character with several losses and gains within the genus. We propose an informal division of the genus based upon five well-supported clades.
Key words: Dichaea, matK, nrITS, Orchidaceae, trnL intron, trnL-F spacer, ycf1, Zygopetalinae
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