BackgroundFloral morphology, particularly the angle of lip attachment to the column, has historically been the fundamental character used in establishing generic limits in subtribe Oncidiinae (Orchidaceae), but it has also been long recognized that reliance on this character alone has produced a highly artificial set of genera. In essence, lip/column relationships reflect syndromes associated with pollinator preferences; most genera of Oncidiinae as previously defined have consisted of a single floral type. Here, the degree to which this has influenced generic delimitation in Brazilian members of the largest genus of Oncidiinae, Oncidium, which previous molecular (DNA) studies have demonstrated to be polyphyletic, is evaluated.MethodsPhylogenetic analyses of the following multiple DNA regions were used: the plastid psbA-trnH intergenic spacer, matK exon and two regions of ycf1 exon and nuclear ribosomal DNA, comprised of the two internal transcribed spacers, ITS1 and ITS2, and the 5·8S gene. Results from all regions analysed separately indicated highly similar relationships, so a combined matrix was analysed.Key ResultsNearly all species groups of Brazilian Oncidium are only distantly related to the type species of the genus, O. altissimum, from the Caribbean. There are two exceptions to this geographical rule: O. baueri is related to the type group and O. orthostates, an isolated species that lacks the defining tabula infrastigmata of Oncidium, is not exclusively related to any previously described genus in the subtribe. Several well-supported subclades can be observed in these results, but they do not correspond well to sections of Oncidium as previously circumscribed or to segregate genera as defined by several recent authors. In spite of their floral differences, these groups of Oncidium, formerly treated as O. sections Barbata, Concoloria pro parte, Crispa, Ranifera, Rhinocerotes, Rostrata (only O. venustum), Synsepala, Verrucituberculata pro parte and Waluewa, form a well-supported clade with Gomesa (including Rodrigueziella and Rodrigueziopsis) embedded in it. Two often recognized segregate genera, Baptistonia and Ornithophora, and the recently described Carriella are also embedded within the Brazilian clade. The level of variation within major subclades of the Gomesa clade is low and similar to that observed within other genera of Oncidiinae.ConclusionsConvergence on a stereotypical syndrome of floral traits associated with pollination by oil-collecting bees has resulted in these characters not being reliable for producing monophyletic taxa, and the genus Oncidium, defined by these characters, is grossly polyphyletic. Vegetative and a few floral/inflorescence characters link these taxa with a mainly Brazilian distribution, and they were all transferred to Gomesa on this basis rather than separated from Gomesa based on their floral differences, which we hypothesize to be simple shifts in pollination strategies. Other authors have described a large number of new genera for these former members of Oncidium, but most of these are not supported by the results presented here (i.e. they are not monophyletic). A new genus, Nohawilliamsia, is described for O. orthostates because it does not fit in any currently recognized genus and is only distantly related to any other member of Oncidiinae.1043387402Castro Neto, V.P., Chiron, G., Deux nouvelles espéces d'Oncidium (Orchidaceae) de Bahia (Bre'sil). (2003) Richardiana, 3, pp. 122-130Castro Neto, V.P., Lacerda Jr, K.G., Carria Castro and Lacerda: A new genus related to Baptisonia Barb. Rodr (2005) Orchids, 74, pp. 692-694Castro Neto, V.P., Lacerda Jr, K.G., (2006) Carriella colorata. Icones Orchidacearum Brasilienses, 2. , t. 123Castro Neto, V.P., Martins Catharino, E.L., Kleberiella et Neoruschia (Orchidaceae, Oncidiinae), deux nouveaux genres extraits du genre (2006) Alatiglossum. Richardiana, 6, pp. 148-160Castro Neto, V.P., Carr, G., Chiron, G., Re'vision du genre Menezesiella Chiron & V.P.Castro (Oncidiinae, Orchidaceae) (2008) Richardiana, 8, pp. 45-69Chase, M.W., A reappraisal of the oncidioid orchids (1986) Systematic Botany, 14, pp. 477-491Chase, M.W., Systematic implications of pollinarium morphology in Oncidium Sw., Odontoglossum Kunth, and allied genera (Orchidaceae) (1987) Lindleyana, 2, pp. 8-28Chase, M.W., Hills, H.G., Silica gel: An ideal desiccant for preserving fieldcollected leaves for use in molecular studies (1991) Taxon, 40, pp. 215-220Chase, M.W., Palmer, J.D., Floral morphology and chromosome number in subtribe Oncidiinae (Orchidaceae): Evolutionary insights from a phylogenetic analysis of chloroplast DNA restriction site variation (1992) Molecular systematics of plants, pp. 324-339. , Soltis DE, Soltis PS, Doyle JJ eds, New York, NY: Chapman and HallChase, M.W., Williams, N.H., Neubig, K.M., Whitten, W.M., Taxonomic transfers in Oncidiinae to accord with Genera Orchidacearum, Volume 5 (2008) Orchids, 77, pp. 20-31Chiron, G.R., Baptistonia Barbosa Rodrigues (Orchidaceae, Oncidiinae): Notes taxinomiques (2008) 2. Richardiana, 8, pp. 111-127Chiron, G.R., Castro Neto, V.P., Contribution à la connaissance des orchide 'es du Bre'sil. III. Re'tablissement du genre Baptistonia Barbosa Rodrigues. (2004) Richardiana, 4, pp. 109-120Chiron, G.R., Castro Neto, V.P., a. Re'vision du genre Baptistonia. 1 (2005) Richardiana, 5, pp. 113-128Chiron, G.R., Castro Neto, V.P., Re'vision du genre Baptistonia. 2 (2005) Richardiana, 5, pp. 169-193Chiron, G.R., Castro Neto, V.P., Menezesiella (Orchidaceae, Oncidiinae), un nouveau genre pour des espèces bre'siliennes bien connues. (2006) Richardiana, 6, pp. 99-106Christenson, E.A., Phymatochilum, un noveau genre monotypique du Bre'sil (Orchidaceae: Oncidiinae) (2005) Richardiana, 5, pp. 194-196van der Cingel, N.A., (2001) An atlas of orchid pollination: America, Africa, Asia and Australia, , Rotterdam: BalkemaDocha Neto, A., Baptista, D.H., Campacci, M.A., Novos gêneros baseados nos Oncidium brasileiros. (2006) Coletânea de OrquI'deas Brasileras, 3, pp. 65-95Doyle, J.J., Doyle, J.L., A rapid DNA isolation procedure for small quantities of fresh leaf tissue (1987) Phytochemical Bulletin, Botanical Society of America, 19, pp. 11-15Dressler, R.L., (1981) The orchids: Natural history and classification, , Cambridge, MA: Harvard University PressDressler RL, Williams NH. 1975. El complejo Oncidoglossum confusum. Orquide'a 4: 752-754Durand, C., Manuel, M., Boudouresque, C.F., Molecular data suggest a hybrid origin for the invasive Caulerpa racemosa (Caulerpales, Chlorophyta) in the Mediterranean Sea (2002) Journal of Evolutionary Biology, 15, pp. 122-133Faria, A., Sistemática filogene'tica e delimitação dos ge'neros da subtribo Oncidiinae (Orchidaceae) endêmicos do Brasil: Baptistonia, Gomesa, Ornithophora, Rodrigueziella, Rodrigueziopsis e (2004) Oncidium pro parte, , PhD thesis, Universidade Estadual de Campinas, São Paulo, BrazilFelsenstein, J., Confidence limits on phylogenies: An approach using the bootstrap (1985) Evolution, 39, pp. 783-791Garay, L.A., Stacy, J.E., Synopsis of the genus Oncidium (1974) Bradea, 1, pp. 393-429Goldblatt, P., Reduction of Barnardiella, Galaxia, Gynandiris, Hexaglottis, Homeria and Roggeveldia in Moraea (Iridaceae: Irideae) (1998) Novon, 8, pp. 371-377Guiard, J., Castroa, un nouveau genre apparente' à Menezesiella (Orchidaceae, Oncidiinae). (2006) Richardiana, 6, pp. 161-164Kelchner, S.A., The evolution of non-coding chloroplast DNA and its application in plant systematics (2000) Annals of the Missouri Botanical Garden, 87, pp. 482-498Königer, W., Weinmann, J.G., A new species of Oncidium from Brazil (1994) Arcula, 2, pp. 50-51Kraenzlin, F., Cyrtochilum (1922) Das Pflanzenreich, , Engler A ed, Leipzig, GermanyNeubig, K.M., Whitten, M.W., Carlsward, B.S., Phylogenetic utility of ycf1 in orchids: A plastid gene more variable than matK (2009) Plant Systematics and Evolution, 277, pp. 75-84Pabst, G.F.J., Dungs, F., (1977) Orchidaceae Brasilienses, , Hildesheim: Brücke Verlagvan der Pijl, L., Dodson, C.H., (1966) Orchid flowers: Their pollination and evolution, , Coral Gables, FL: University of Miami PressPolanco, C., Gonzáles, A.I., de la Fuente, A., Dover, G.A., Multigene family of ribosomal DNA in Drosophila melanogaster reveals contrasting patterns of homogenization for IGS and ITS spacer regions: A possible mechanism to resolve this paradox (1998) Genetics, 149, pp. 243-256Powell, M., (2008) Evolutionary ecology of Neotropical orchids, with an emphasis on Oncidiinae, , PhD Thesis, University of Reading, UKPridgeon, A.M., Cribb, P.J., Chase, M.W., Rasmussen, F.N., Genera orchidacearum. Vol. 5. Epidendroideae (part two). Oxford: Oxford University Press (in press).Reis MG, Marsaioli AJ, Faria AD, Amaral MCE, Bittrich V. 2000. The chemistry of flower rewards - Oncidium (Orchidaceae) (2009) Journal of the Brazilian Chemical Society, 11, pp. 600-608Romowicz, A., Szlachetko, D.L., Genera et species orchidalium. 12. Oncidieae (2006) Polish Botanical Journal, 51, pp. 43-47Sanford, W.W., Sexual compatibility relationships in Oncidium and related genera (1964) American Orchid Society Bulletin, 33, pp. 1035-1048Sanford, W.W., Sexual compatibility relationships in Oncidium and related genera. II (1967) American Orchid Society Bulletin, 36, pp. 114-122Swofford, D.L., (2001) PAUP* 4.0: Phylogenetic analysis using parsimony (* and other methods), , Sunderland, MA: Sinauer AssociatesSzlachetko, D.L., Systema orchidalium (1995) Fragmenta Floristica et Geobotanica Supplementum, 3, pp. 1-152Szlachetko, D.L., Genera et species orchidalium. 11. Oncidieae (2006) Polish Botanical Journal, 51, pp. 39-41Szlachetko, D.L., Mytnik-Ejsmont, J., Genera et species orchidalium. 13. Oncidieae (2006) Polish Botanical Journal, 51, pp. 49-51Whitten, M.W., Williams, N.H., Chase, M.W., Subtribal and generic relationships of Maxillarieae (Orchidaceae) with emphasis on Stanhopeinae: Combined molecular evidence (2000) American Journal of Botany, 87, pp. 1842-1856Williams, N.H., Chase, M.W., Fulcher, T., Whitten, W.M., Molecular systematics of the Oncidiinae based on evidence from four DNA regions: Expanded circumscriptions of Cyrtochilum, Erycina, Otoglossum and Trichocentrum and a new genus (Orchidaceae) (2001) Lindleyana, 16, pp. 113-139Williams, N.H., Chase, M.W., Whitten, W.M., Phylogenetic positions of Miltoniopsis, Caucaea, a new genus Cyrtochiloides, and Oncidum phymatochilum (Orchidaceae: Oncidiinae) based on nuclear and plastid DNA data (2001) Lindleyana, 16, pp. 272-285Xu, D.H., Abe, J., Sakai, M., Kanazawa, A., Shimamoto, Y., Sequence variation of non-coding regions of chloroplast DNA of soybean and related wild species and its implications for the evolution of different chloroplast haplotypes (2000) Theoretical and Applied Genetics, 101, pp. 724-732