Tropical Asian Origin, boreotropical migration and long-distance dispersal in Nettles (Urticeae, Urticaceae).

The tribe Urticeae (Urticaceae), popularly known as Nettles, include 12 genera and ca. 200 species, constituting a diverse and cosmopolitan plant clade centered in tropical Asia, Africa, and South America. The global distribution of this clade makes it an excellent group to test hypotheses regarding the processes underlying tropical intercontinental disjunctions. More specifically, it allows us to test whether current distribution patterns resulted from recent transoceanic long-distance dispersal or ancient vicariance after boreotropical migration. We reconstructed the phylogeny of Nettles with the nuclear ITS and four plastid DNA regions (rbcL, trnL-F, matK and rpl14-rpl36) using Bayesian inference and maximum parsimony approaches. We inferred divergence times using a Bayesian uncorrelated lognormal relaxed molecular clock model and ancestral areas using the divergence-extinction-cladogenesis (DEC) model. Our results indicate a tropical Asian origin for the tribe during the late Paleocene. Migration events to Eurasia, South America and Africa occurred mainly during the Oligocene and Miocene. However, several long-distance dispersal events, including dispersals from Asia to Hawaii or Australasia, were inferred to have occurred from the Miocene onwards. The fleshy fruits and winged diaspores of several taxa are suited for long-distance dispersal.