Ammi majus (Apiaceae), naturalized as a field weed in Belgium. – The distribution and status in Belgium and the neighbouring countries of the annual umbellifer Ammi majus have been investigated using recent observations. This Mediterranean and South Atlantic species has recently become naturalized, mainly in Flanders and in parts of Wallonia, except south of the rivers Sambre and Meuse. The recent data show that the species has mainly become naturalized in arable fields and field edges. The species also occurs as small ephemeral populations along roads and waterways. The most likely hypothesis to explain its occurrence in both environments is the application on fields of animal slurry or manure from animals (e.g. fowl) that were fed on grain that contains seeds of A. majus. The occurrences along roads and waterways could be an indirect effect of this pathway by washing off of manure, but they may also be due to spilling of seeds during grain transportation.