1. Increasing landscape heterogeneity and organic farming practices are known to enhance species richness in agroecosystems. However, little is known about the consequences of these management options on other biodiversity components such as community composition, phylogenetic structure and functional diversity which may be more closely linked to ecosystem functioning. 2. We surveyed semi-natural plant communities within the uncultivated field margins of 18 arable farms in Skåne, south Sweden. We investigated how taxonomic, phylogenetic and functional diversity responds to landscape heterogeneity (presence of semi-natural habitat) and farm management intensity (organic vs. conventional farming). 3. Plant species richness and functional diversity metrics all responded positively to landscape heterogeneity, with the strongest effect occurring on conventional farms. Community composition differed with farm management, and mean phylogenetic relatedness, an indicator of phylogenetic structure, was significantly higher on the field margins of organic compared to conventional farms. Individual plant functional groups themselves responded in unique ways to land management and landscape heterogeneity. 4. Synthesis and applications. Management strategies that promote the conservation of heterogeneous landscapes (i.e. a higher proportion of semi-natural habitats) and organic farm management practices are important for maintaining plant phylogenetic, functional and taxonomic diversity in agroecosystems. Accommodating various forms of diversity is important to ensure that ecosystems have the greatest possible array of species ecologies'. Such measures will help to improve the capacity of these ecosystems to provide multiple ecosystem functions, including the sustaining and regulating services of benefit to people.