Abstract
Ph.D. (Botany)
Several studies have focussed on Combretaceae, however, phylogenetic relationships still remain unresolved within certain groups in the family. This study represents the most comprehensive phylogenetic inference using molecular data from both plastid (rbcL, matK, trnH-psbA, and psaA-ycf3) and nuclear nrITS regions. The phylogeny of Combretaceae was used to examine relationships, test biogeographic hypotheses, infer divergence age estimates for major lineages and explore the influence of dispersal, vicariance and extinction in shaping the current intercontinental disjunct distribution. The sister position of Combretaceae to the rest of the order Myrtales is supported with two distinct subfamilies, Combretoideae and Strephonematoideae. Monophyly of tribe Laguncularieae was observed with Macropteranthes, a genus endemic to Australia, included. Within tribe Combreteae, two subtribes are distinguished, Combretineae and Terminaliinae, with Gueira and Calycopteris sister to subtribe Combretineae. Two clades, within genus Combretum were noted, subgenus Combretum and Cacoucia with Meiostemon sister to subgenus Combretum. Within subtribe Terminaliinae, Terminalia is observed to be paraphylectic with two main clades distinguished. Clade I comprised of Old World and a few New World species, while clade II is mainly comprised of New World species and a few Old World species. Within clade II, genera Buchenavia, Anogeissus, Bucida, and Pteleopsis are embedded within Terminalia. Conocarpus is sister to clade II. This result allowed the formal transfer of the genera Anogeissus, Buchenavia, and Pteleopsis into Terminalia.
Abstract
Divergence times were estimated using the Bayesian MCMC approach implemented in BEAST, suggesting a crown date for Combretaceae of ca, 110 mya, corresponding to the split of the two subfamilies during the Late Cretaceous period. Ancestral area reconstructions inferred using RASP and DEC model (Lagrange), suggested a Gondwanan origin for Combretaceae, with long - distance dispersal as the major event to account for the current intercontinental disjunct distribution pattern.
Finally, the use of DNA barcoding is proposed as a complementary tool for species discrimination and identification, in addition to traditional morphological approaches. Core barcodes (rbcLa + matK) with the addition of trnH-psbA were identified as the best barcodes for the family Combretaceae.