Small grassland patches are hotspots for medicinal plants and associated phytochemical diversity in European agricultural landscapes
O_LIMedicinal plants are threatened by overcollection and habitat loss due to human activities. In this study, we aimed to reveal how ancient earthen burial mounds covered with successional grasslands of different ages can contribute to conservation of medicinal plants and related phytochemical diversity in European agricultural landscapes. C_LIO_LIUsing vegetation data collected from 166 mounds in Hungary, we identified the medicinal plant species present at these sites, and based on multiple literature sources, provided the secondary metabolite profiles of the medicinal plants and plant communities. By using generalized linear mixed models and redundancy analysis we investigated how the age of the vegetation, percentage of croplands around the sites, site area, and soil properties influence the diversity of medicinal plants and associated phytochemicals. C_LIO_LIWe found that mounds provide safe havens for a wide range of medicinal plants and secondary metabolites. Our results showed that grassland-related medicinal plants producing iridoids and diterpenes were typical on mounds with older grasslands. A large proportion of croplands in the neighboring landscape and high soil pH supported generalist medicinal plants producing nitrogen-containing and sesquiterpene related secondary metabolites. Higher soil nitrogen, phosphorus, and potassium content favored medicinal plants producing lignans, glycosides, and organic acids. C_LIO_LIOur results suggest that the high phytochemical diversity is supported by the occurrence of various compounds facilitating the adaptation of medicinal plants to the various environmental stressors and biotic factors, such as competition, herbivory and pathogens, present in sites embedded in agricultural landscapes. C_LI Societal Impact StatementBesides being important components of landscape-level biodiversity, medicinal plants are essential resources for traditional and modern healthcare. However, in parallel with biodiversity loss driven by human activities, populations of medicinal plants have also declined. By maintaining connections between nature, culture, and people, sacred natural sites can help counteract this trend. We studied the potential of ancient burial mounds to maintain populations of medicinal plants and related phytochemical diversity in European agricultural landscapes. Our findings highlight the importance of conserving grassland vegetation and associated biodiversity at these sites, which is crucial for preserving a key ecosystem service in intensively managed landscapes.