AOBPreview originally published online on August 7, 2008
Annals of Botany 2008 102(4):491-507; doi:10.1093/aob/mcn128
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Molecular Phylogeny of the Neotropical Genus Christensonella (Orchidaceae, Maxillariinae): Species Delimitation and Insights into Chromosome Evolution
1 Department of Botany, Biology Institute, P.O. Box 6109, University of Campinas, UNICAMP, 13083-970, Brazil
2 Departamento de Botânica, Centro de Ciências Biológicas, Universidade Federal de Pernambuco, Recife, PE, 50670-420, Brazil
3 Florida Museum of Natural History, University of Florida, Dickinson Hall, Gainesville, FL, 32611-7800, USA
4 Departamento de Botânica, IB, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, 91501-970, Brazil
5 Department of Genetics and Evolution, Biology Institute, P.O. Box 6109, University of Campinas, UNICAMP, 13083-970, Brazil
* For correspondence. Present address: Departamento de Genética, Universidade de São Paulo/ESALQ, Caixa Postal 83, Piracicaba, SP, 13400-970, Brasil. E-mail skoehler{at}esalq.usp.br
Received: 5 October 2007 Returned for revision: 18 March 2008 Accepted: 23 June 2008 Published electronically: 7 August 2008
Background and Aims: Species' boundaries applied within Christensonella have varied due to the continuous pattern of variation and mosaic distribution of diagnostic characters. The main goals of this study were to revise the species' delimitation and propose a more stable classification for this genus. In order to achieve these aims phylogenetic relationships were inferred using DNA sequence data and cytological diversity within Christensonella was examined based on chromosome counts and heterochromatin patterns. The results presented describe sets of diagnostic morphological characters that can be used for species' identification.
Methods: Phylogenetic studies were based on sequence data of nuclear and plastid regions, analysed using maximum parsimony and maximum likelihood criteria. Cytogenetic observations of mitotic cells were conducted using CMA and DAPI fluorochromes.
Key Results: Six of 21 currently accepted species were recovered. The results also support recognition of the ‘C. pumila’ clade as a single species. Molecular phylogenetic relationships within the ‘C. acicularis–C. madida’ and ‘C. ferdinandiana–C. neowiedii’ species' complexes were not resolved and require further study. Deeper relationships were incongruent between plastid and nuclear trees, but with no strong bootstrap support for either, except for the position of C. vernicosa. Cytogenetic data indicated chromosome numbers of 2n = 36, 38 and 76, and with substantial variation in the presence and location of CMA/DAPI heterochromatin bands.
Conclusions: The recognition of ten species of Christensonella is proposed according to the molecular and cytogenetic patterns observed. In addition, diagnostic morphological characters are presented for each recognized species. Banding patterns and chromosome counts suggest the occurrence of centric fusion/fission events, especially for C. ferdinandiana. The results suggest that 2n = 36 karyotypes evolved from 2n = 38 through descendent dysploidy. Patterns of heterochromatin distribution and other karyotypic data proved to be a valuable source of information to understand evolutionary patterns within Maxillariinae orchids.
Key words: Chromosome number, Christensonella, Cymbidieae, cytotaxonomy, fluorochrome staining, Maxillaria, Maxillariinae, molecular phylogenetics, species delimitation
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