Abstract/Summary

Fabales is a cosmopolitan angiosperm order which consists of four families, Leguminosae (Fabaceae), Polygalaceae, Surianaceae and Quillajaceae. Despite the great interest of botanists, a convincing phylogeny of the order is still not available because almost every phylogenetic study reveals a different scheme of relationships amongst families of the order. Therefore, this work is centred on the possible causes of these discrepancies in order to determine a more robust topology. Not only supermatrix analyses with 678 taxa, but also phylogenetic analyses with nuclear gene sequences are performed here for the first time. Additional analyses, such as simulations, network analyses, sampling different outgroups (random or real) and molecular clock rooting to both identify any long branch attraction and/or rooting problems were also employed. These analyses clearly show that the Fabales phylogeny has been influenced by sampling of outgroups, tree reconstruction methods and data sampling. However, network analyses show that even though it is weak, there is a consistent phylogenetic signal among the rapidly radiated Fabales families, which can be traced by further analyses. Moreover, molecular clock rooting analysis yielded a (((Quillajaceae+Surianaceae)Polygalaceae)Leguminosae) topology with strong support for the first time here. This thesis also explores an evolutionary question using the new phylogeny presented here. Evolution of keel flowers within Fabales is explored to investigate a possible “benefit scenario” suggested to account for the origin of these flower types within two species-rich families of Fabales, Polygalaceae and Leguminosae. Results of molecular dating, ancestral area, ancestral state (habit and inflorescence size) and particularly floral size analyses revealed that this “benefit scenario” may or may not be a plausible explanation for the convergent evolution of keel flowers in Polygalaceae and Leguminosae within Fabales, because the picture that emerges from the current study is a complicated one.