| Prunus is one of the largest and most important genera in the Rosaceae family. Its species include peaches, almonds, cherries, plums and apricots. The genus is extremely diverse and its species are found from subartic habitats to the tropics. Species of Prunus are traditionally classified into six subgenera. Subgenus Padus is characterized by bearing leafy racemes and Laurocerasus by its leafless racemes. The rest of the subgenera, Emplectocladus, Cerasus, Amygdalus, and Prunus are defined by a combination of characters. Phylogenetic relationships of the genus are examined by parsimony, maximum likelihood and Bayesian analyses of the cpDNA trnL-trnF spacer and the nuclear regions ITS and s6pdh, a gene that codes for sorbitol-6-phosphate dehydrogenase. Cerasus, excluding section Microcerasus , and Prunus are monophyletic. Padus and Laurocerasus are most likely paraphyletic to the rest of the genus. However, there are considerable differences between results from cpDNA, which is maternally inherited in Prunus, and nuclear ITS. These differences could be due to a history of hybridization that gave rise to extant lineages. Character evolution on the phylogenies produced by the ITS data show that the traits used to segregate Padus and Laurocerasus are considerably homoplastic and some may have arisen as adaptations. A clade consisting of subgenera Emplectocladus, Prunus, Amygdalus and section Microcerasus , is supported by all data sets and it is characterized by a derived arrangement of the axillary buds in groups of three. This Glade also has the greatest diversity in reproductive characters, such as the multiple and independent evolution of dry and pubescent fruits, and widespread occurrence of tubular hypanthia. Despite the consistent support by multiple data sets, there is some phylogenetic uncertainty regarding relationships within this Glade. This is because some branches of the trees are excessively short perhaps due to slower rates of evolution, adaptive radiation, or both. The lack of closely related outgroups to Prunus complicated homology assessment of molecular and non-molecular data. This work identified the major Glades in Prunus and set the guidelines for a more comprehensive study that should include species not available for this dissertation. |
