Of the 9 tribes in Apocynaceae-Apocynoideae, the Echiteae is a group of lianas (rarely erect herbs) and comprises 19 genera and about 200 species, of which 16 genera are restricted to the Neotropics. The tribe Echiteae was proposed more than 120 years ago, but its composition has varied through time. The results of some phylogenetic studies have suggested that the tribe is non-monophyletic, a condition also applying to of its genera in the present circumscription. In this work, we provide the first phylogenetic study of the Echiteae, using nuclear (ITS) and chloroplast markers, in order to test the monophyly of the tribe and its subtribes, analyzing the largest dataset ever compiled. The results show that Echiteae and four of its subtribes (Echitinae, Parsonsiinae, Peltastinae and Prestoniinae) as previously circumscribed are non-monophyletic. The fifth subtribe, Pentalinoninae, though monophyletic, does not belong to Echiteae; Prestonia and Temnadenia are resolved as polyphyletic, whereas Fernaldia is nested within Echites and Peltastes is nested in Macropharynx, and therefore, these two genera are reduced to synonymy. Fourteen genera are maintained and a new subtribe Laubertinae is proposed. In the ancestors of Echiteae, we hypothesize that an evolutionary shift took place in which steroidal alkaloids and/or cardenolides, characteristic for apocynoids, were replaced by parsonsine type pyrrolizidine alkaloids as the henceforth predominant chemical defense compounds. Prestonia is the second largest genus of Echiteae, with ca. 56 species distributed in Tropical America and the West Indies. The last monograph was published in 1936, but it is out of date due the number of species described since then. Only synopsis for some areas and flora treatments are available. Preliminary phylogenetic studies have suggested that the genus is not monophyletic. At the same time, four infrageneric classifications proposals have been published, but never have been tested with molecular data. Therefore, the circumscription of Prestonia and the relationships between the species remained unresolved. Two phylogenetic analyses using chloroplast (trnL intron and trnL-trnF intergenic spacer, rpl16 intron, rps16 intron, matK and 3′ / 5′ trnK intron) and nuclear data (ITS) were conducted for Prestonia with three aims: 1) to determine if the genus is monophyletic and to establish its relationships with the others genera in the tribe Echiteae, 2) to evaluate the current infrageneric classification proposals, as well as to determine the interspecific relationship in Prestonia, 3) to provide the necessary nomenclatural and / or taxonomic changes. The results of the present thesis show that Prestonia in the previous circumscription was polyphyletic, because P. riedelii is sister to Rhodocalyx and Temnadenia ornata is nested inside Prestonia. In consequence, the first species was transferred to Rhodocalyx and the second species to Prestonia. In the second part of the study and with a larger sampling, Prestonia could be shown to be monophyletic, but the sections proposed by Schumann, Woodson or Pichon are non-monophyletic. A new infrageneric classification is proposed, recognizing six sections: Coalitae, Denticulata, Exsertae, Haemadictyon, Mollis, and Prestonia.

As result of this study, the first synopsis of Prestonia for Colombia (the second most diverse country in South America) recognizing 25 species was published. And finally, this thesis is proposing a new monograph for Prestonia, with 56 species currently accepted. Descriptions, illustrations, distribution maps and IUCN conservation criteria are provided for every species. A key to the species is presented and the 6500 herbarium specimens examined were assigned to species and annotated.