Orchid Biology: Darwin`s Contrivances 150 Years Later
Freudenstein, John .
A supermatrix analysis of the large orchid subfamily Epidendroideae.
Although a great deal of progress has been made over the last two decades in resolving relationships among subfamilies and tribes of orchids, the Epidendroideae has remained problematic, especially with respect to resolving the relationships among tribal-level groups, many of which are themselves well resolved and strongly supported. This may well be due to a rapid radiation at the base of the epidendroids that resulted in short branches, but understanding the reason for the problem does not lessen our need for this resolution to allow us to trace evolution of key characters in the subfamily. In this analysis, a supermatrix dataset of eight loci was assembled for over 300 genera of epidendroids, utilizing outgroups from the other subfamilies. In many cases, synthetic terminals were created that comprised more than one species per genus. The loci comprised nuclear (ITS, Xdh), plastid (trnLF, matK, rbcL, psaB, ycf1) and mitochondrial sequences (nad1b-c intron). Parsimony and likelihood analyses resulted in very similar highly resolved trees; resampling support analyses revealed good support for many groups not previously resolved, while leaving some parts of the tree without supported resolution. Strongly supported clades allow several major conclusions to be drawn. First, the small, largely temperate tribe Neottieae is sister to the remainder of the subfamily. Several other lineages of “primitive” epidendroids, including Sobraliinae, Triphoreae, and Tropidieae fall between Neottieae and the “advanced” epidendroids, the latter comprising the well-supported remainder of the subfamily. Second, the vandoid morphology, which characterizes many epidendroid groups that have the most highly specialized pollinium transfer systems, has evolved three times – in Vandeae, Calypsoeae, and Cymbidieae/Maxillarieae. Third, the structure within the “advanced” epidendroids is remarkably correlated with a few Old World-New World shifts, suggesting that the overall pattern of diversification in the subfamily was dominated by a small number of major vicariant or dispersal events, followed by extensive radiations. A number of smaller dispersal events was probably responsible for the remainder of the distributional patterns observed. Finally, the distribution of leafless epidendroids on the tree suggests at least 20 independent losses of leaves in the subfamily.
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1 - Ohio State University, Herbarium, Dept. of Evolution, Ecology and Organismal Biology, 1315 Kinnear Road, Columbus, OH, 43212, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Franklin B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 3:15 PM