This thesis presents the first monographic taxonomic treatment of Vicia in South America, in which 20 native species are recognized. In addition to an identification key, the taxonomic account provides full synonymy, and for each species a detailed description, distribution map, notes on distribution, habitat, phenology and an IUCN conservation assessment. Vicia buchtienii P.Hechenleitner is described as new, V. bidentata Hook. is reinstated as a separate species, and the new combination of V. bonariensis (Burkart) P.Hechenleitner is made. Fifteen names are newly reduced to synonymy, 23 lectotypes are chosen, and one neotype is proposed. Four of the 20 species are considered endangered. South American Vicia species are assigned to section Australes. Based on Bayesian and parsimony analysis of DNA sequence data from chloroplast (matK and psba-trnH) and nuclear ribosomal internal transcribed spacer (ITS) sequences representing 50% of the species of Vicia in South America, sect. Australes is shown to be paraphyletic. If classification is to reflect monophyly, sect. Australes should be expanded to include three north and central American species that are nested within it. The phylogenetic results suggest a single origin of Vicia in South America resulting from long-distance dispersal from North America. A densely sampled species-level phylogeny of sect. Australes was estimated using nuclear (ITS) and chloroplast (psbA-trnH) regions analysed using Bayesian and parsimony approaches. Fourteen of the 20 South American Vicia species were included, many represented by multiple accessions, resulting in the most comprehensive phylogenetic study of the section to date. Vicia minutifora D.Dietr. is the probable sister to the remaining species in sect. Australes, and the lack of geographic structure in the phylogeny implies repeated dispersal events within South America. By revealing three probable new species from Peru and Bolivia, the phylogeny indicates the utility of combining phylogenetic and morphological analyses in the delimitation of closely related species.

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