Phylogeny and historical biogeography of Phylanthaceae

The main objective of this proposal is investigation of historical biogeography of the family Phyllanthaceae. This family was earlier considered to be a subfamily of Euphorbiaceae, the sixth largest plant family. Phyllanthaceae are a pantropical family with 58 genera and approximately 2000 species. Most of these genera have widely disjunct distributions, e.g. Amanoa, Andrachne, Flueggea and Meineckia. Detailed distribution data at the generic level are available for this family in RBG Kew. None of these widely disjunct genera has any apparent adaptation to long dispersal. Dispite this important geographic disjunction on different taxonomic levels no analysis of historical biogeography has yet been done. In our investigations we construct a molecular phylogeny based on various plastid (rbcL, atpB and matK) and nuclear (26S and phyC) markers having a minimum of two taxa per genus. Plastid rbcL and atpB genes have already been sequenced for 20 taxa in a preliminary investigation. In the case of genera with a large number of species such as Phyllanthus, infrageneric variation will be studied using rapidly evolving spacer regions in the plastid genome as well as using nuclear ribosomal (ITS) internal transcribed spacer regions. This will be paralleled by a morphology based phylogenetic tree. In addition to this informations available on pollen morphology, seed morphology and seed anatomy will be combined with our data sets. This molecular plus the macro- and mico morphology based phylogentic trees will be used to analyse the historical biogeography of this family. Biogeographical analysis will be undertaken both with an area-based approach using the program COMPONENT, and with a taxon-based approach using the recently developed programme DIVA. Timing of branching patterns will be evaluated for species occurring on isolated volcanic islands and this will establish the maximum age for the node within the phylogenetic tree and hence a calibration point for a molecular clock. From this the ages of the taxa on continental areas can be extrapolated.

Phyllanthaceae are one of five segregates of Euphorbiaceae sensu lato recognised at family level by the Angiosperm Phylogeny group. The family contains c.2000 species in 59 genera. A new classification is done for this family based on the molecular studies using DNA sequence data of nuclear PHYC and plastid atpB, matK, ndhF and rbcL in conjuction with morphological characters. One of the major contribution from our molecular phylogeny is the division of the family into two strongly supported clades which represents the two subfamilies Antidesmatoideae and Phyllanthoideae and ten tribes. Further, Phylogenetic relationships within tribe Phyllantheae, the largest tribe of the family Phyllanthaceae, were examined with special emphasis on Phyllanthus which is one of the economically important genus. ITS nuclear ribosomal and plastid matK DNA sequence data for roughly 100 species of tribe Phyllantheae were analyzed including representatives of all published subgenera of Phyllanthus .We recognize six lineages at generic rank in tribe Phyllantheae: Flueggea s.l., Lingelsheimia, Margaritaria, Phyllanthus s.l., Plagiocladus, and Savia section Heterosavia. Richeriella should be united with Flueggea, and the generic status of Plagiocladus (= Phyllanthus diandrus) is confirmed. Results confirm paraphyly of Phyllanthus having Breynia, Glochidion, Reverchonia, and Sauropus embedded within. Phyllanthus maderaspatensis is sister to all other species of Phyllanthus s.l., and the genus appears to be of Old World origin. The unique branching architecture, "phyllanthoid branching", of most Phyllanthus taxa has been lost (and/or has evolved) repeatedly. Taxonomic divisions based on similar pollen morphology are largely confirmed, and related taxa share similar distributions. Ancestral areas were reconstructed from one of the most parsimonious tree, using MP analysis from the combined data with the DIVA program, version 1.1 Current distribution areas for the genera of Phyllanthaceae were coded in eight categories (Asia, Africa, Australia, Madagascar, Mediterranean, North America, South America, and West Indies). The relative timing shows that this family originated from Africa, but further work on divergence time using fossil record from a related family (Clusiaceae) is in progress and this will be published soon.