Questions Small, remnant habitats embedded in degraded, human-dominated landscapes are generally not a priority in conservation, despite their potential role in supporting landscape-scale biodiversity. To warrant their inclusion in conservation management and policy, we question under which conditions they may exhibit the largest conservation value. Location Nine landscapes spread across the counties of Stockholm and Sodermanland, Sweden. Methods Per landscape, plant communities were surveyed in 6 and 12 1 x 1 m(2) plots across large, intact semi-natural grasslands and small remnant grasslands, respectively. These two contrasting grassland types served as a model system. A topsoil sample was taken in each plot to determine habitat quality in terms of soil pH, plant-available P, and C:N ratio. We used a joint species distribution model to analyse the extent to which grassland type and habitat quality define and predict resident community diversity and composition, including whether they support grassland specialists. Results At the landscape scale, the combined remnant grasslands sustained diverse plant communities which did include a significant subset of habitat specialists. Yet, the contribution of individual remnants clearly varied with local-scale habitat quality; soil phosphorus availability lowered plot-level species richness, mostly by constraining the occurrence of grassland specialists. Semi-natural grassland communities were comparatively insensitive to variation in soil phosphorus availability. Conclusions The combined habitat amount and the significant number of habitat specialists sustained by remnant grasslands with high habitat quality, shows they can represent a valuable resource to support landscape-scale biodiversity conservation. This offers no wildcard to neglect the continued biotic and abiotic threats on semi-natural grassland plant diversity such as chronic and accumulating P eutrophication, discontinuation of management or poor matrix permeability, as semi-natural grasslands harbour the majority of habitat specialists, while sourcing surrounding remnant grassland communities.