The distributions of naturalised alien plant species that have invaded natural or semi-natural habitat are often
geographically restricted by the environmental conditions in their new range, implying that alien species with similar
environmental requirements and tolerances may form assemblages and characterise particular areas. The aim of this study
was to use objective numerical techniques to reveal any possible alien phytogeographic regions (i.e. geographic areas with
characteristic alien plant assemblages) in southern Africa. Quarter degree resolution presence records of naturalised alien
plant species of South Africa, Lesotho, Swaziland, Namibia and Botswana were analysed through a divisive hierarchical
classification technique, and the output was plotted on maps for further interpretation. The analyses revealed two main
alien phytogeographic regions that could be subdivided into eight lower level phytogeographic regions. Along with
knowledge of the environmental requirements of the characteristic species and supported by further statistical analyses, we
hypothesised on the main drivers of alien phytogeographic regions, and suggest that environmental features such as
climate and associated biomes were most important, followed by human activities that modify climatic and vegetation
features, such as irrigation and agriculture. Most of the characteristic species are not currently well-known as invasive plant
species, but many may have potential to become troublesome in the future. Considering the possibility of biotic
homogenization, these findings have implications for predicting the characteristics of the plant assemblages of the future.
However, the relatively low quality of the dataset necessitates further more in-depth studies with improved data before the
findings could be directly beneficial for management.