Over three decades of research on adventive plants associated with grain and oilseed imports in Belgium —so-called “grain aliens”— have revealed shifting patterns in species composition. In recent years, several taxa have emerged that are inconsistent with the presumed geographic origin of the imported grain. Notably, southern African weeds such as Oncosiphon pilulifer and Arctotheca calendula are now regularly encountered, despite the apparent absence of grain imports from southern Africa. Inquiries indicate that a substantial increase in grain shipments has occurred from Australia, with Ukraine being a secondary source. Until recently, however, no unequivocally Australian arable weeds had been identified at transshipment sites. The 2024 discovery of Eragrostis parviflora — a species endemic to Australia and not naturalized elsewhere — provides a direct indication of introduction via Australian grain imports. Another striking case is Panicum gilvum, a southern African species long naturalized in Australian croplands and first identified in Belgium in 2024 on a grain unloading quay. Subsequent investigations revealed that P. gilvum has in fact been established in Belgian maize fields since at least two decades, but went unnoticed due to confusion with P. dichotomiflorum. The species’ belated recognition in Belgium, together with its prominence as an arable weed in Australia, points to Australian grain as the likely vector of introduction. These observations may also shed new light on the true origin of another South African weed, Panicum schinzii, which has been established in Belgian maize fields for years and is likewise naturalized in Australia. This paper explores these findings in detail and discusses their implications for understanding global trade pathways and the biogeography of alien plant species.