Tanacetum balsamita L. (syn.: Balsamita major Desf., Chrysanthemum balsamita (L.) Baillon) (SW-As.) – A very rare and ephemeral garden escape or garden throw-out. First recorded in 1941 along a railway track in Chokier. Subsequently seen in Châtelet (1948), Diegem (1983) and Hologne-sur-Heer (1989). Most recently observed in Bure (Tellin) in 2016 and on the exposed banks of river Maas in 2020. Apparently much decreasing in cultivation nowadays.
Tanacetum balsamita is most often seen with rayless heads. The plants recently observed along river Maas, however, have white ligules. Such plants belong to subsp. balsamitoides (Sch.-Bip.) Grierson and are perhaps worth specific rank (T. balsamitoides Sch.-Bip.; see E+M Plantbase). Photos of these plants are available here: https://waarnemingen.be/observation/193380180/.
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