Phylogenomics, Biogeography, and Taxonomy of Senna (Leguminosae, Caesalpinioideae).

Abstract

The legume genus Senna comprises more than 300 species that have colonized a wide range of habitats, from deserts and seasonally dry tropical forests to wet tropical forests and savannas, from sea level to nearly 4,000 m in the Andes. The genus is notable for its long history of human use, with medicinal applications documented since at least the ninth century AD, as well as numerous ornamental species cultivated worldwide and invasive species that affect natural ecosystems and agriculture. The flowers of Senna display a set of morphological and functional traits associated with buzz pollination, which have been the subject of extensive study in the last two decades. Despite this attention, significant gaps remain about the taxonomic and evolutionary knowledge of Senna, including problematic species complexes, undescribed species, the absence of a comprehensive phylogenetic analysis, and the lack of studies on its biogeographic history across continents. In this context, my thesis addresses these gaps through an integrated approach. Chapter I presents the most comprehensive phylogenomic analysis of Senna to date, covering approximately 86% of the species in the genus, together with a new infrageneric classification and a synthesis of current knowledge on the genus, including updated information on diversity, ecology, evolution, and human uses. Chapter II provides the first comprehensive biogeographic analysis of Senna, examining the role of transoceanic long-distance dispersal in shaping its pantropical distribution. Chapters III–VI comprise taxonomic studies focused on Neotropical species of Senna, including integrative studies of species complexes based on genomic and morphometric data, comprehensive taxonomic revisions, and the description of seven new species. Finally, an Appendix includes a co-authored paper addressing the phylogeny and taxonomy of the tribe Cassieae, to which Senna belongs. Together, these studies provide a fundamental contribution to the taxonomy and evolutionary understanding of Senna and establish a framework for future research, conservation, and sustainable use of the species of Senna.