Edaphically unusual sites harbor a flora that is often unique in its taxonomic as well as functional composition and contain many endemic species. While this edaphic endemism, edaphism, has been discussed previously on various special soils, in this study we relate it for the first time to the floristic characteristics of so called “quartz islands”, edaphically driven special habitats in South Africa, and their surroundings (matrix habitat). We sampled the vegetation and soil for 245 vegetation plots in the Knersvlakte Nature Reserve and examined 336 plant species with respect to their evolutionary (plant family, habitat specificity), biogeographical (distributional range) as well as functional traits (life form, leaf succulence, flowering onset, dispersal mode). Based on the floristic uniqueness of the quartz islands, we expect them to host a highly specialized and locally endemic flora with smaller life forms, pronounced leaf succulence (both indicative of resource-conservative economics) and distinct reproductive traits than their surroundings. We find that, compared to the matrix habitat, quartz islands have significantly higher salinity and lower soil pH, and show higher proportion of leaf-succulent species of smaller life forms – some of which are restricted to quartz islands and have different timing of flowering onset, while dispersal via zoochory is less important. Like other special soils, quartz islands harbor unique plant species, which are distinguished by distinct trait patterns. We conclude that the concept of edaphism can be applied to quartz islands.