Floristic composition of 14 mesas (i.e. flat-top mountains) in four different study areas was investigated in southern African Nama Karoo. The study areas were arranged along a latitude gradient. Two simple questions were asked: are mesas potential conservation islands (a) in terms of re-colonization potential and (b) in terms of species richness? Detailed vegetation surveys along a transect from the plains to the top of each mesa were summarized to obtain species composition for the three main habitats: plain, slopes and plateau. Floristic similarities between plains and mesa habitats were used to answer question (a), and species richness was used to answer question (b). Geographic position, high within-area variability and elevation were found to largely influence the findings, resulting in only few consistent trends. Keywords: arid lands, island biogeography, Namibia.