| Summary: | <p>Phylogenetic studies on the genus <em>Ipomoea</em>, and specifically on the species closely related to the sweet potato, have been hindered by limited taxon and character sampling. Any study that aims to investigate the phylogenetic relationships within a megadiverse genus such as <em>Ipomoea</em>, with an estimated 800 species, must rely on a comprehensive data set that covers as much diversity as possible, in order to provide accurate and robust phylogenetic inference.</p> <p>In this thesis, I present a comprehensive phylogenetic study of the genus <em>Ipomoea</em> and of the group of species closely related to the sweet potato using genomic-scale data. The aim of this study was to provide a phylogenetic framework with which to understand the diversity existing within the genus and to inform taxonomic decisions. The phylogenies presented here identify several recurrent patterns in the evolution of <em>Ipomoea</em>, for instance the multiple origin of storage roots and the existence of multiple episodes of long-distance dispersal by natural means.</p> <p>I also address several questions pertaining to the sweet potato that have been a matter of debate for decades but remained unanswered until recently. Our genome-scale data facilitated comprehensive phylogenies for all wild species that are most closely related to the sweet potato. Our phylogenies resolve that sweet potato is monophyletic and had a single origin, as well as identified the wild species that is its closest relative: <em>Ipomoea trifida</em>, with all other extant species more distantly related. In addition, our studies corroborate the existence of two sweet potato chloroplast lineages and infer that one of them resulted from a hybridisation between sweet potato and <em>I. trifida</em> following species divergence.</p> <p>Finally, I also address a question that has been of interest for over two centuries: the presence of the sweet potato, an American crop, in Polynesia in pre-European times.</p>
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