Abstract

The theories that explain the origin and evolution of the pantropical tree family Dipterocarpaceae have long been controversial, with two alternative hypotheses of Gondwanic origin and vicariance or Eurasian origin and dispersal. To test these two hypotheses, I have inferred the divergence dates of major clades through molecular phylogenetic and dating analyses using the nucleotide sequences of the chloroplast matK gene and fossil data of 49 dipterocarp species. Phylogenetic analyses produced highly consistent, well-resolved tree topologies with molecular clocklike evolution up to the level of the genera and sections. Independent calibration points based on dipterocarp fossil data were used to calibrate the molecular clock. The results revealed the early Cretaceous Gondwanic origin of the family and the radiation of the Pakaraimoideae (121-117 Mya), mid to late Cretaceous radiation of the Monotoideae (117-88 Mya) and the late Cretaceous to early Eocene origin and diversification of the Dipterocarpoideae (88-54 Mya). The rate of nucleotide substitution of the matK gene in dipterocarps is 2.5 {604} 10 -10 per synonymous site per year. The absolute age estimates showed a gradual pattern of speciation in agreement with the "museum hypothesis" up to the level of genera and sections. The results were highly congruent with the paleogeographical and paleoclimatic events, morphological and ecological evidence. This study supports the view that ancestral stocks of dipterocarpoids dispersed from the African to Deccan plate and subsequently dispersed to the Eurasian plate and diversified in Southeast Asia giving rise to the present day species richness in the far eastern rain forests.