title: Lessons from Plectocephalus (Compositae, Cardueae-Centaureinae): ITS disorientation in annuals and Beringian dispersal as revealed by molecular analyses.
abstract: OBJECTIVE
  The geographic distribution of the genus Plectocephalus comprises a single species in Ethiopia, two in North America and possibly four more in South America, in a striking disjunction that is exceptional for genera of the tribe Cardueae. The enormity of this disjunction cast doubts on the precise taxonomic delineation of the genus, which is not unanimously recognized as a natural entity. The aims of this study were to define the generic boundaries of Plectocephalus and to formulate a hypothesis that would explain its natural range.
  
  
  METHODS
  A combined molecular approach, using nuclear internal transcribed spacers (ITS) and external transcribed spacers (ETS), and plastid trnL-trnL-F, rpl32-trnL(UAG) and ndhF markers, was chosen for phylogenetic reconstruction by maximum parsimony and Bayesian inference.
  
  
  RESULTS
  Phylogenetic analysis shows that Plectocephalus is a natural genus that includes the African species P. varians, together with all the native South American species, currently classified as Centaurea, C. cachinalensis, C. floccosa and C. tweediei. The recognition of Centaurodendron as an independent genus, which we consider appropriate, would make Plectocephalus paraphyletic. Affinities of Plectocephalus should lie with eastern representatives of Centaureinae. Geographic disjunction is explained as a consequence of dispersal via the Bering Land Bridge during the Miocene--Pliocene. The phylogeny of the basal grade of Centaureinae differs from previous phylogenies, and artefacts resulting from differences in mutation rates of annual and perennial taxa are confirmed. Sensitivity of ITS to these differences was the highest observed for all DNA regions used in this study.
  
  
  CONCLUSIONS
  The natural status of the genus Plectocephalus is confirmed and several nomenclatural combinations are proposed. New evidence contributes to the debate concerning problems posed by the use of ITS in the phylogenetic reconstruction of groups that differ in terms of their life cycles. Dispersal from Caucasus and Anatolia along the Siberian route and then across the Bering Land Bridge follows a route previously proposed for other taxonomic groups.
authors.affiliation: Botanic Institute of Barcelona (IBB-CSIC-ICUB), Pg. del Migdia s/n, E08038 Barcelona, Spain. asusanna@ibb.csic.es
authors.forename: Alfonso
authors.initials: A
authors.lastname: Susanna
authors.forename: Mercè
authors.initials: M
authors.lastname: Galbany-Casals
authors.forename: Konstantyn
authors.initials: K
authors.lastname: Romaschenko
authors.forename: Laia
authors.initials: L
authors.lastname: Barres
authors.forename: Joan
authors.initials: J
authors.lastname: Martín
authors.forename: Núria
authors.initials: N
authors.lastname: Garcia-Jacas
mesh_terms: D019659:Asteraceae / Q000145:classification / Q000235:genetics*; D031179:Centaurea / Q000145:classification / Q000235:genetics; D018742:DNA, Chloroplast / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D005843:Geography; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D018742:DNA, Chloroplast; D021901:DNA, Intergenic; D018744:DNA, Plant