<p><i>Buddleja davidii</i> Franch. is a Chinese ornamental plant that has become successfully naturalised and potentially invasive in most of Europe over the past century. Regarded as a species of unstable and disturbed sites, its ecological niche, invasiveness, and syntaxonomy have often been overlooked. In this study, we examined plant communities in which the species occurs in Slovenia and Europe using multivariate methods, focusing on differences in their ecology, taxonomical and functional diversity. To evaluate the invasiveness potential of <i>B. davidii</i> in communities it inhabits, we tested the extent to which its cover explains variation in Shannon–Wiener’s diversity index, evenness, disturbance severity and frequency indices, proportions of life forms, Grime’s life strategies and neophytes’ cover and number, using linear regression. Our results show that <i>B. davidii</i> has its ecological optimum in various types of shrub communities, primarily in riparian zones and abandoned quarries, which represent newly proposed subassociations of the typical <i>Buddlejetum</i> association. Communities with <i>B. davidii</i> can withstand varying levels of disturbance and generally consist of species with a competitive life strategy, while the most dominant life forms are hemicryptophytes and phanerophytes. Increasing cover of <i>B. davidii</i> accounted for little variation in taxonomical and functional diversity, and this effect was the most prominent in riparian shrub communities, followed by the <i>Buddlejetum</i> association and communities on wall crevices. Occurrences in different plant communities confirm the species’ ecological plasticity, whereas its invasiveness is relative, due to its limited relationship with the diversity parameters.</p>