Calendula arvensis L. (Medit., Macar., SW-As.) – A rare and much decreasing, ephemeral alien. First collected around 1859 in Saint-Denis. In the first half of the 20th century recorded as a grain alien at a mill in Lessive in 1940 and 1941 and as a weed of agricultural fields in Rochefort in 1941. Also seen on waste land in Vierset-Barse in 1947. Since 2013 known from a tramway track in Jette (Brussels). In this locality Calendula arvensis grows with several tens in bare, gravelly soil, produces a lot of seed and seems to persist well.
The distinction between Calendula arvensis and C. officinalis is usually easy. However, more or less intermediate plants sometimes occur.
Hilger H.H. & Reese H. (1983) Ontogenie der Strahlblüten und der heterokarpen Achänen von Calendula arvensis (Asteraceae). Beitr. Biol. Pfl. 58(1): 123-147.
Reichert H. (1959) Über einige Vorkommen von Calendula arvensis L. im nördlichen Rheinhessen. Hessische Floristische Briefe 8: 399-400.