title: The Tetramerium lineage (Acanthaceae: Justicieae) does not support the Pleistocene Arc hypothesis for South American seasonally dry forests.
abstract: OBJECTIVE
  The Tetramerium lineage (Acanthaceae) presents a striking ecological structuring in South America, with groups concentrated in moist forests or in seasonally dry forests. In this study, we investigate the circumscription and relationships of the South American genera as a basis for better understanding historic interactions between dry and moist biomes in the Neotropics.
  
  
  METHODS
  We dated the ancestral distribution of the Tetramerium lineage based on one nuclear and four plastid DNA regions. Maximum parsimony, maximum likelihood, and Bayesian inference analyses were performed for this study using 104 terminals. Phylogenetic divergences were dated using a relaxed molecular clock approach and ancestral distributions obtained from dispersal-vicariance analyses.
  
  
  RESULTS
  The genera Pachystachys, Schaueria, and Thyrsacanthus are nonmonophyletic. A dry forest lineage dispersed from North America to South America and reached the southwestern part of the continent between the end of the Miocene and beginning of the Pleistocene. This period coincides with the segregation between Amazonian and Atlantic moist forests that established the geographic structure currently found in the group.
  
  
  CONCLUSIONS
  The South American genera Pachystachys, Schaueria, and Thyrsacanthus need to be recircumscribed. The congruence among biogeographical events found for the Tetramerium lineage suggests that the dry forest centers currently dispersed throughout South America are relatively old remnants, probably isolated since the Neogene, much earlier than the Last Glacial Maximum postulated by the Pleistocene Arc hypothesis. In addition to exploring the Pleistocene Arc hypothesis, this research also informs evolution in a lineage with numerous geographically restricted and threatened species.
authors.affiliation: Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Av. Transnordestina s/n, Novo Horizonte 44036-900, Feira de Santana, Bahia, Brazil.
authors.forename: Ana Luiza A
authors.initials: AL
authors.lastname: Côrtes
authors.affiliation: Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Av. Transnordestina s/n, Novo Horizonte 44036-900, Feira de Santana, Bahia, Brazil.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rapini
authors.affiliation: Department of Botany, California Academy of Sciences, 55 Music Concourse Dr., Golden Gate Park, San Francisco, California 94118 USA.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Daniel
mesh_terms: D027901:Acanthaceae / Q000145:classification*; D001499:Bayes Theorem; D016001:Confidence Intervals; D003890:Desiccation; D065928:Forests; D008954:Models, Biological; D010802:Phylogeny; D012621:Seasons; D013020:South America; D013997:Time Factors
keywords: Amazonian forest; Atlantic forest; Neotropics; biogeography; phylogenetics; refuges