Phylogenetic relationships of the vanilloid orchids: An integration of molecular, morphological, and anatomical data

Analyses of 175 rbcL sequences from Orchidaceae were completed. Results indicate that the family is divided into five subfamilial clades: apostasioid, cypripedioid, orchidoid, epidendroid and vanilloid orchids. The vanilloid orchids (Vanilleae sensu Dressler, 1980) can further be divided into a subclade corresponding to genera of Pogoniinae and a subclade that includes genera from Vanillinae and Galeolinae. In all rbcL trees, the following vanilloid units are monophyletic: Pogoniinae, Pogonia, temperate Pogoniinae, Vanilla, Epistephium, Eriaxis with Clematepistephium, and genera from Galeolinae.; 18S nrDNA gene sequences were then completed for 25 orchid taxa and compared to the rbcL topologies. Results of this study indicate that Orchidaceae is divided into the same five subfamilial clades as discovered with rbcL, including a vanilloid clade. Moreover, 18S provides data placing the achlorophyllous genus Lecanorchis in that vanilloid clade.; Sequences from the ITS region provided a third set of molecular data. Alignments of ITS 1 and 2 were met with difficulty, and results from analyses of computer-generated alignments conflict with rbcL and 18S trees. Only the 5.8S gene can be aligned with confidence, although alone it is not sufficient to resolve relationships among the vanilloid orchids.; As the rbcL, 18S, and ITS molecular analyses suggest the monophyly of winged seeds, reticulate leaf venation, and pollinia among the vanilloid orchids, these morphological characters were investigated further. Seed coat studies by SEM reveal structural diversity from tunicate seeds to multi-layered, sclerotic seeds with or without wings among the vanilloids, and easily distinguish the genera from one another. Cleared leaves from several vanilloid taxa exhibit convergent evolution toward reticulate dicot-like venation from typically monocotyledonous patterns. Pollen ultrastructure examined by TEM demonstrates the existence of a tubular intine and reduced exine in some vanilloids that shed their pollen as free monads; a trend toward pollinia formation is evident in the group.; Finally, characters from the three molecules were combined with forty-eight morphological characters. Results of these total evidence analyses do not strongly conflict with the topologies produced from independent data analyses, but are somewhat inconclusive in constructing exact inter-generic relationships for the vanilloid orchids.