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The occurrence and diversity of Prunus outside of temperate North America and Eurasia has been frequently overlooked. Particularly, the Neotropics has been the region where the taxonomic knowledge of the genus was weaker with just few reports of new species and only one historical revision (Koehne, 1915). A taxonomic synopsis of all the evergreen taxa of Prunus currently in the Americas is presented in chapter 1 based on an exhaustive specimen revision comprising 8322 individual specimens (duplicates) corresponding to 4146 distinct botanical records housed in 94 herbaria from the Americas and Europe. A total of 246 taxa of Prunus (all with racemose inflorescences) comprising 227 species (plus the generally naturalized or cultivated P. serotina) were identified in the New World. 97 taxa with already published legitimate basionyms were accepted (out of a total 110 basionyms) and 149 taxa were identified as taxonomic novelties. After these results, the genus, traditionally considered a typical temperate taxon, now amounts its highest diversity in the tropics and particularly in the New World side. The higher number of novelties were found in the Andes, a region with a considerable environmental diversity but also with most of its ecosystems highly fragmented and adversely impacted by human activities. As part of the taxonomic studies, a full taxonomic treatment of the species of Mesoamerica was done in chapter 2 derived and complemented from a published Spanish version created during this research (Pérez-Zabala, 2015). Most of the species in Mesoamerica were previously known only by one or few specimens and since non taxonomic revision had been previously done, most specimens in herbaria (the larger portion collected in the last 40 years) remained as unidentified or misidentified. As a result, 31 species were identified and fully described for the region, including 3 cultivated and one commonly naturalized. Additionally, 11 species were recognized as novelties to science (yet to be published), lectotypes were designated for 5 species, and 4 previously published names were categorized as synonyms. Following this study, Prunus was confirmed as the more diverse genus of Rosaceae (among 20 genera) in Mesoamerica.In chapter 3, the phylogeny and evolution of the environmental niche in terms of the water regime preference was investigated across the genus considering a better representation of Neotropical species, a group that generally was absent or scarcely sampled in previous studies. Prunus, as an almost cosmopolitan group, exhibits a wide variety of habitat preference and many species are recognized because the tolerance to seasonality of water availability (by dryness or freeze), some with the ability to resist extreme conditions as desertic or high elevation places. In the Neotropics, even though many species are distributed in humid places, a considerable number also occupy geographic pockets of seasonally dry forest, rocky outcrops, and rain shadow patches. The best supported BEAST phylogeny suggested the split of the genus in two main clades similarly to previous studies. One comprising mostly deciduous species with solitary flower, corymbs, or racemes, plus some evergreen racemose but pubescent, leaf domatia-bearing, or with deciduous calyx. The other clade included the evergreen, glabrous and racemose species which are mostly tropical and marginally subtropical. The Neotropical species were recovered as polyphyletic with two small groups in the first clade and most of the species in a single clade within the evergreen racemose main clade. However, inconsistences between trees inferred from nuclear and plastid regions were observed as in other studies, which suggests ancient introgressions in the racemose lineages of the first clade. Evolution of hydraulic niche (in terms of aridity index) was significantly correlated with the phylogeny and main monophyletic groups have an identifiable range of hydraulic tolerance. The current geographic wide spread of the genus seems to be favored by a retention of tolerance to water stress which even so was not identified as an evolutionary limiting factor that impeded the adaptation to a wide variety of water regimes. Future studies about the evolution of geography, ecology and functional traits in Prunus should involve a greater number of tropical species considering the appreciable weight in its diversity. A better knowledge of the tropical species can effectively contribute to their conservation and additionally could contribute to improve the understanding of the response to environmental stress of economically appreciated species in cultivation.

Supplementary materials:1. One PDF file including: 1. The best RAxML maximum likelihood tree based on the combined DNA dataset, 2. The best supported Bayesian phylogenetic tree based on the chloroplast DNA dataset, 3. The MaxEnt response curves for each species created using the variable Aridity Index, 4. The predicted maps of geographic distribution for each species modeled by MaxEnt based on predicted niche suitability, 5. The DNA alignment of 2166 bp in nexus format of the combined dataset with all the species, 6. The DNA alignment of 1871 bp in nexus format of the combined dataset with the selected species used for the comparative analyses. 7. The R script implemented for the comparative analyses of niche evolution. 2. One MS Excel files including: 1. MaxEnt niche modeling results for each species, 2. The correlation data matrices (one for all the species, and another for the Neotropical ones) of niche overlap measured with the metrics I (lower triangle) and D (upper triangle) (Species are organized following the phylogeny and data are visualized in Fig 3.4 and Fig. 3.5).