Phylogenetic analysis of morphology in Prunus reveals extensive homoplasy

Prunus is a large and economically important genus with considerable morphological variation. The evolution of vegetative and reproductive characters are examined here by parsimony reconstruction on trees obtained from data of ITS, trnL-trnF, trnS-trnG, and 25 morphological characters of 37 species of Prunus and representatives of eight other genera of Rosaceae. Prunus grayana is supported as the sister species to the rest of Prunus and the common ancestor of Prunus is reconstructed as having deciduous and serrated leaves, leafy racemes and fruit with well-developed pericarp. All diagnostic characters used in classification of the raceme-bearing species show some degree of convergent evolution and do not reflect phylogenetic relatedness. Some character states, such as evergreen foliage and entire leaf margin, are likely adaptations to environments with higher humidity and mean temperature. However, these hypotheses need to be tested by including species formerly classified in genus Pygeum, which were not available for this study. A clade consisting of subgenera Prunus, Amygdalus, Emplectocladus and section Microcerasus (formerly in subgenus Cerasus) is characterized by having axillary buds organized in groups of three, two of which give rise to flowers or inflorescences and one to a vegetative shoot. Fruits with thin pericarps are common in Prunus but they arose more than once independently. Dry fruits also evolved more than once, and only in species of Prunus living in arid environments, suggesting that this feature is another example of adaptation. Maddenia hypoleuca is nested within Prunus and the morphological characters used to segregate it from Prunus have been misinterpreted or are also found in species of Prunus previously classified in genus Pygeum.