Molecular Phylogentics Systematics in Dendrobieae (Orchidaceae)

Molecular systematic research, using DNA sequences of the internal transcribed spacer (ITS) region of the 18-26S nuclear ribosomal repeat unit, was conducted on a broadly representative sample of the tribe Dendrobieae. The results provide independent support, in addition to evidence from plastid DNA analysis and morphology, for the phylogenetic reassessment of the taxon. At a broad level, Dendrobieae are polyphyletic with Dendrobium sect. Oxystophyllum being deeply embedded within one of the outgroup taxa, subtribe Eriinae: Podochileae. The remaining taxa form a weakly supported monophyletic group consisting of three major clades, Epigeneium, sister to predominantly Asian and Australasian clades. This author has formally recognized these as Epigeneiinae, Dendrobiinae s.s., and Grastidiinae, respectively. Detailed studies using species representative of all major historical taxonomic groups within those subtribes provide strong support for the continued recognition of the genera Cadetia, Diplocaulobium, and Flickingeria, all of which are deeply embedded within Grastidiinae and far removed from Dendrobium s.s. in Dendrobiinae. These studies have also identified numerous other strongly supported clades that group species predominantly on the basis of synapomorphic vegetative rather than floral characters. The recognition of these morphologically distinct monophyletic groups as genera is considered to be phylogenetically more informative, predictive, and realistic than any of the previously offered alternatives.