Oxalis corniculata and its close relatives are found in every country in the world and are significant weeds of horticulture. Yet it is not known where they came from originally and their taxonomy and nomenclature is a frequent cause of disagreement. We are making a global assessment of the Oxalis corniculata group with specimens from as much of its global range as possible. We will use a molecular phylogenetic approach, as well as using morphology and cytology to understand how this group has evolved and how it has been so successful.