1. Helianthus annuus L. (N-Am., Mex.) – A very common but always ephemeral alien. The first herbarium collection was made remarkably late: first collected in 1915 in Antwerpen and Hoboken (on wasteland and as a weed in a beet field). Subsequently found in widely scattered localities in large parts of Belgium (perhaps less frequently in Wallonia). Helianthus annuus is usually introduced as a commercial oilseed or as birdseed and readily germinates where-ever seeds are spilled. It formerly also occurred along river Vesdre near Verviers, possibly as a wool alien. Nowadays it is most frequent in port areas (near unloading quays and conveyors, on wasteland near granaries, along railway tracks,…), along motorways or as a birdseed alien in urban areas and on dumps. It is often cultivated as an ornamental in gardens and might occur as a garden escape as well.
Helianthus annuus is a rather variable species but attempts to produce a widely adopted infraspecific classification failed (Schilling 2006).
Schilling E.E. (2006) Helianthus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 21. Oxford University Press, New York-Oxford: 141-169.