Molecular phylogenetics of Diseae (Orchidaceae): a contribution from nuclear ribosomal ITS sequences

We present here the first molecular phylogeny of tribe Diseae (Orchidoideae: Orchidaceae). Nuclear ribosomal ITS1, 5.8S rDNA, and ITS2 sequences were compared for 30 Diseae, 20 Orchideae, and four Cranichideae and Diurideae outgroups. ITS - rDNA sequences exhibited a transition:transversion ratio of 1.3 and extensive ITS length polymorphism. Phylogenetic analyses using maximum parsimony identified seven major core orchidoid groups. The branching order of the five Diseae and two Orchideae clades was weakly supported but indicated paraphyly of Diseae, with Disperis sister to the rest, followed by successive divergence of Brownleea, Disinae, Coryciinae sensu stricto (s.s.), Satyriinae, and terminated by Orchidinae plus Habenariinae. Within the monophyletic Disinae, Herschelia and Monadenia were nested within a paraphyletic Disa and clustered with D. sect. Micranthae. Within monophyletic Satyriinae, Satyridium rostratum plus Satyrium bicallosum was sister to the rest of Satyrium, and then Satyrium nepalense plus S. odorum was distinct from a cluster of six species. Coryciinae are paraphyletic because Disperis is sister to all other core orchidoids. Coryciinae s.s. are sister to Satyriinae plus Orchideae, with Pterygodium nested within Corycium. Maximum likelihood analysis supported possible affinities among Disinae, Brownleeinae, and Coryciinae but did not support monophyly of Diseae or an affinity between Disinae and Satyriinae. Morphological characters are fully congruent with the well-supported groups identified in the ITS phylogeny.