title: Molecular phylogeny of the neotropical genus Christensonella (Orchidaceae, Maxillariinae): species delimitation and insights into chromosome evolution.
abstract: OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Department of Botany, Biology Institute, P.O. Box 6109, University of Campinas, UNICAMP, 13083-970, Brazil. skoehler@esalq.usp.br
authors.forename: Samantha
authors.initials: S
authors.lastname: Koehler
authors.forename: Juliano S
authors.initials: JS
authors.lastname: Cabral
authors.forename: W Mark
authors.initials: WM
authors.lastname: Whitten
authors.forename: Norris H
authors.initials: NH
authors.lastname: Williams
authors.forename: Rodrigo B
authors.initials: RB
authors.lastname: Singer
authors.forename: Kurt M
authors.initials: KM
authors.lastname: Neubig
authors.forename: Marcelo
authors.initials: M
authors.lastname: Guerra
authors.forename: Anete P
authors.initials: AP
authors.lastname: Souza
authors.forename: Maria do Carmo E
authors.initials: Mdo C
authors.lastname: Amaral
mesh_terms: D002871:Chromosome Banding; D032461:Chromosomes, Plant; D018744:DNA, Plant / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D019143:Evolution, Molecular; D007621:Karyotyping; D016013:Likelihood Functions; D029595:Orchidaceae / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D018087:Plastids / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer