title: Old-New World and trans-African disjunctions of Thamnosma (Rutaceae): intercontinental long-distance dispersal and local differentiation in the succulent biome.
abstract: OBJECTIVE
  The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we used Thamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra.
  
  
  METHODS
  We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange.
  
  
  RESULTS
  Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene.
  
  
  CONCLUSIONS
  We conclude that the Old-New World disjunction of Thamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of Thamnosma.
authors: Botany Department, State Museum of Natural History Stuttgart, Rosenstein 1, Stuttgart, Germany. mike.thiv@smns-bw.de
authors: Mike
authors: M
authors: Thiv
authors: Timotheüs
authors: T
authors: van der Niet
authors: Frank
authors: F
authors: Rutschmann
authors: Mats
authors: M
authors: Thulin
authors: Thomas
authors: T
authors: Brune
authors: Hans Peter
authors: HP
authors: Linder