Microclimates are crucial for understanding plants and how they respond to climate change and land use change, however, microclimates are often overlooked in many ecological studies and assessments. Here, we analysed how microclimatic temperatures and soil moisture influence plant diversity in mountain grasslands in southern Africa. We used field-quantified data on taxonomic and functional diversity and microclimates, and we show that plant diversity is influenced by these microclimates that vary at high spatial and temporal scales. These findings are based on our field data from thousands of plots across three distinct grasslands on a 1-km elevational gradient at the Drakensberg mountain range. We recorded continuous microclimate observations that cover a range of typical mountain grassland conditions, including frost and fire events and diurnal ranges of over 40 C. Our findings indicate that the detected plant diversity patterns are influenced by microclimates in various ways. Our results strengthen the ecological and microclimatic understanding of these mountain grasslands where biodiversity is at severe risk due to rapid climate change and land use change.