Maxillarieae

Abstract: The monophyly of and phylogenetic relationships within the orchid tribe Maxillarieae Pfitzer were evaluated using parsimony analyses of combined nuclear ribosomal and plastid DNA sequence data of ITS 1 and 2, matK, and the trnL intron and the trnL-F intergene spacer. Each of the separate analyses produced highly congruent but weakly supported patterns (by the bootstrap), so these were combined in a single analysis. Analysis of 90 ingroup taxa (representing ;35% of currently recognized genera) and four outgroup taxa produced resolved and highly supported cladograms. Based on the cladograms, we recognize six subtribes: Eriopsidinae, Oncidiinae (including Pachyphyllinae, Ornithocephalinae, and Telipogoninae), Stanhopeinae, Coeliopsidinae, Maxillariinae (including Lycastinae and Bifrenariinae), and Zygopetalinae (including Cryptarrheninae, Dichaeinae, Huntleyinae, and Warreinae). Stanhopeinae were sampled most intensively; their generic relationships were highly resolved in the analysis and largely agree with currently accepted generic concepts based on morphology. Coeliopsidinae (Coeliopsis, Lycomormium, Peristeria ) are sister to Stanhopeinae. Correlations are drawn among phylogeny, pollination mechanisms, and life history traits. Tribe Maxillarieae Pfitzer sensu Dressler (1993) consist of ;2600 species in ;165 genera (;10% of Orchidaceae) and contain many of the showy epiphytic orchids of the Neotropics including horticulturally important genera such as Lycaste Lindl., Oncidium Sw., OdontoglossumKunth, Stanhopea Frost ex Hook., and Zygopetalum Lindl. The tribe includes most Neotropical orchids possessing a complex pollinarium with a viscidium and stipe, pseudobulbs usually of a single internode, and the Maxillaria seed type (Barthlott and Ziegler, 1981; Chase and Pippin, 1987). They have highly diverse vegetative habits, floral morphology, and pollination mechanisms. Within Maxillarieae, subtribe Stanhopeinae contain some of the most exotic pollination mechanisms found in orchids (Darwin, 1877; van der Pijl and Dodson, 1966). They are pollinated exclusively by male euglossine bees collecting fragrant chemicals from the flowers, and their complex floral shapes manipulate the bees to place pollinaria on precise locations on the bee’s body. We now know a considerable amount about the pollination biology of Stanhopeinae from the fieldwork of Dodson, Dressler, and others, but understanding the evolution of pollination-related traits requires a reliable phylogeny. In this study, we present analyses of Maxillarieae based on combined analyses of nuclear and plastid regions. Early in the course of our analyses of Stanhopeinae, we concluded that the choice of outgroups was problematic because an explicitly