<p>This study examines the weediness potential of spontaneous vegetation in an agroecosystem undergoing an agroecological transition in Buenos Aires Province, Argentina. We sampled parcels under three types of agronomic management—conventional, agroecological with annual crops and agroecological with perennial crops—along with non-managed terraces. We assessed floristic and functional diversity based on seven traits associated with weediness: clonality, growth form, life cycle, dispersal syndrome, plant fecundity, maximum potential vegetation height, and seed size. In floristic terms, a principal component analysis clearly separated the parcels into three distinct groups: terrace, conventionally managed, and agroecological. The weediness potential of spontaneous vegetation showed distinct differences across the types of land management. Conventional parcels were characterized mainly by high-weediness species (non-clonal annuals, herbaceous, with high fecundity and having small seeds) whereas terrace parcels were characterized by low-weediness species (shrubby perennials with hemerochoric dispersal, low fecundity and large seeds). Agroecological parcels exhibited mixed weediness traits, and those with annual crops were largely composed of herbaceous non-clonal annuals with intermediate traits and hemerochoric dispersal. Agroecological parcels with perennial crops featured mainly graminoids, annuals and stoloniferous species with intermediate traits. Consequently, terrace parcels are unlikely to contribute significantly to common weedy vegetation. Understanding functional traits related to the weediness of spontaneous vegetation is essential for agriculture, as it can help promote beneficial species and control harmful ones, supporting the transition to agroecological practices and improving ecosystem processes while reducing pesticide use.</p>