Guizotia is an African genus of at least six species (probably more according to recent phylogenetic research; see Geleta & al. 2010). One species, Guizotia abyssinica, is more or less widely cultivated as an oilseed crop, especially in the (sub-) tropics. However, experimental fields are also found in Belgium. Its seed (Niger seed) also is a major component in commercial birdseed mixtures.
Most species of Guizotia are much alike in general appearance. A second taxon, Guizotia scabra (Vis.) Chiov. subsp. schimperi (Schultz-Bip.) J. Baagøe (syn.: G. schimperi Schultz-Bip.), is the most closely related to G. abyssinica (Tadesse 1999, Geleta & al. 2010) and might have been overlooked. It was recently recorded in Germany (Savelsbergh & al. 1991). It is best distinguished by its smaller achenes (2-2,5 mm versus 3-6 mm), outer involucral bracts ovate and apparently 1-nerved (versus broadly ovate and ca. (5-)9(-12)-nerved) and glandular hairy receptacular paleae. It is a weedy species that often grows together with Guizotia abyssinica and might as well be introduced with it.
References
Baagøe J. (1974) The genus Guizotia (Compositae). A taxonomic revision. Bot. Tidsskr. 69: 1-39.
Geleta M., Bekele E., Dagne K. & Bryngelsson T. (2010) Phylogenetics and taxonomic delimitation of the genus Guizotia (Asteraceae) based on sequences derived from various chloroplast DNA regions. Plant Syst. Evol. 289: 77-89.
Savelsbergh E., Savelsbergh I. & Geerlings J. (1991) Spatherbst 1990 mit interessanten Adventivpflanzen im Aachener Stadtbereich Rothe Erde (TK 25 5202/232 und /241). Flor. Rundbr. 25(1): 46-53.
Tadesse M. (1999) New combinations, varieties and synonyms in African Compositae. Compositae Newsletter 33: 23-32. [available online at: http://www.biodiversitylibrary.org/item/48867#page/25/mode/1up].