Systematics, biogeography and petiole anatomy of Sabiaceae with emphasis on Meliosma

The focus of this dissertation is the evolutionary history of the plant family Sabiaceae, with emphasis on the genus Meliosma. The goals of the first chapter were to test monophyly of the three genera in the family, as well as to infer relationships among them and among subclades in Meliosma. Parametric and non-parametric analyses of nuclear and chloroplast sequence data revealed that the two other genera in the family, Sabia and Ophiocaryon, are monophyletic, but that Meliosma is probably not monophyletic due to Ophiocaryon being nested within it. Further, phylogenetic results indicate that Sabia is the first-diverging lineage in the family, and that the branching pattern within Meliosma is highly congruent with its subgeneric classification, which is based on endocarp morphological characters. Chapter two presents a biogeographic study of Sabiaceae, including consideration of the fossil record of Meliosma and Sabia. The estimated ages of three fossils were selected as time constraints to conduct divergence time estimation analyses; these results were coupled with those of geographic range evolution analyses to illuminate the biogeography of this group in space and time. Results indicate that Sabiaceae diverged shortly after the diversification of other basal eudicots, and that Sabia and Meliosma have an Asian origin. In addition, results suggest that several lineages within Sabiaceae were widely distributed throughout the Northern Hemisphere during the Eocene, a time when global temperatures were warmer at higher latitudes, and that Meliosma most likely reached the New World through the North Atlantic Land Bridge. Results are not conclusive as to how Meliosma arrived to South America, but suggest that it was already there by the early Miocene; after this the two most species-rich clades in Meliosma diversified in the Andes and Central America. The third chapter includes an anatomical study of leaf petioles, which have a distinctive cylindrical shape in Meliosma. Results indicate petioles in Meliosma are not pulvini as those found in other plant groups such as Fabaceae. Moreover, petiole anatomy is most similar between Meliosma and Ophiocaryon, supporting the hypothesis that these two genera are more closely related to each other than either one is to Sabia..