Rosette‐shaped plants can amplify the diversity of predator arthropods and act as potential shelters for these animals in grassland ecosystems under grazing effect. Here we evaluated the contribution of a vertical rosette‐shaped plant (Eryngium horridum) to patterns of spider diversity and functional traits in subtropical grasslands under different grazing intensities. We used a common sub‐shrub (Baccharis crispa) and the herbaceous vegetation as reference microhabitats. Sampling was conducted in 23 plots described according to grazing intensity based on environmental co‐variables. Spiders were sampled with D‐Vac suction within patches of E. horridum, B. crispa, and the herbaceous vegetation. Compared to the reference microhabitats, E. horridum harboured distinct community composition with a subset of exclusive species, and morphologically adapted spiders. Spider richness increased in Eryngium plants as grazing pressure increased and the grassland became more simplified. Abundance of runners and space web‐builders responded in a similar fashion, while orb‐web builders were more abundant in E. horridum regardless of grazing intensity. Our results indicate that these rosette plants positively affect top invertebrate predators, with a special role for sites with high grazing intensities where it promotes microhabitat complexity and aggregates more individuals and species. Thus, grassland management that alter Eryngium's occurrence must be conducted cautiously.