Phylogenetic relationships of Pogoniinae (Vanilloideae, Orchidaceae): An herbaceous example of the Eastern North America-Eastern Asia phytogeographic disjunction

Phylogenetic relationships within subtribe Pogoniinae (Vanilloideae: Orchidaceae) are evaluated with analyses of plastid rbcL DNA sequences, nuclear ribosomal TTS DNA sequences, morphology, and combined evidence. All these matrices produced patterns that agree on the broader phylogenetic relationship within the clade. Duckeella is sister to all Pogoniinae, South American species of Cleistes are monophyletic, Pogonia is monophyletic and part of a larger clade of temperate taxa (Isotria, Pogonia, and Cleistes divaricata) from North America and Asia. The structure of the cladograms and the high levels of bootstrap support strongly indicate that the genus Cleistes is paraphyletic. The disjunction between tropical South American and temperate North American taxa as well as the disjunction between Pogonia ophioglossoides in eastern North America with P. minor and P. japonica in eastern Asia are best explained by speciation following a northward long-distance dispersal and subsequent northwestward migration via Bering land bridges in the Tertiary. This phylogenetic study adds an additional herbaceous example to the growing list of plants that demonstrate this classical biogeographic pattern.