Communal rangelands are losing biodiversity and ecosystem function due to land clearing, deforestation, and climate change. However, mistletoes can enhance plant communities by increasing litterfall, soil moisture, and soil fertility. This study examined the effects of mistletoe infection (uninfected, low, and high) on Sclerocarya birrea subsp. caffra understorey plant assemblages, herbaceous biomass, and herbivory across three sites with different rainfall levels (590 mm, 655 mm, and 695 mm). At the broader community scale, species composition varied significantly across sites, but remained similar across mistletoe infection levels. At a fine, species level scale, the mistletoephily index showed species-specific preferences for different infection levels. The intermediate rainfall site had lower total species richness, diversity, and grass diversity than the other sites. Herbaceous biomass was higher in the wetter than the drier site, while forb and tree richness and diversity were greater in the drier site. Mistletoe infection and its interaction with rainfall site significantly influenced grass and forb diversity. Our findings suggest that moisture is limiting, typical of semi-arid savannas, while mistletoe effects are additive. Therefore, rainfall site influences host tree resource acquisition and competition, shaping understorey plant heterogeneity, while mistletoes provide additional facilitative effects that may further enhance communal rangeland resilience.