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Abstract Aim Plant–plant interactions are an important factor in structuring plant biodiversity. However, most studies on the impacts of plant–plant interactions on biodiversity focus on species richness and to a lesser extent on other facets of diversity. When other facets of biodiversity are considered, studies often include a limited set of environmental conditions. We aimed to quantify the impacts of nurse plants on taxonomic, functional and phylogenetic facets of plant biodiversity and how these impacts change across environmental gradients. Location We report data on 28 alpine and 50 dryland sites, established in 11 countries. Time period 1998–2019. Major taxa studied Vascular plants. Methods We analysed plant–plant interactions using co‐occurrence analyses and obtained information on the functional traits and phylogenetic relationships of the beneficiary species. We calculated the change in taxonomic, functional and phylogenetic diversity caused by the presence of nurse plants and environmental conditions. Results Nurse plants enhanced taxonomic and phylogenetic diversity in alpine communities and enhanced functional and phylogenetic diversity in dryland communities. However, they had a positive effect on functional and taxonomic diversity only in moderate environments in alpine and dryland communities, respectively. The effects of nurse plants were larger in drylands for functional and phylogenetic diversity and in alpine communities for taxonomic diversity. Interestingly, nurse plants induced nonlinear changes in all facets of biodiversity across environmental gradients, whereas biodiversity tended to increase linearly toward more benign conditions in open interspaces. Main conclusions Facilitation is important in alpine environments to maximize taxonomic diversity and has a more consistent positive effect on the functional and phylogenetic diversity of drylands. In general, effects of facilitation on biodiversity peak in moderate environmental conditions, which suggests that nurse plants can protect biodiversity from impacts of climate change mostly in those places currently under low environmental stress and that will be likely to experience moderate stress levels in the future.