Leonurus japonicus Houtt. (syn.: L. heterophyllus Sweet, L. artemisia (Lour.) S.Y. Hu, L. sibiricus auct. non L.) (E-As.) – A very rare and ephemeral alien. First recorded on a compost heap (as a weed) in the former botanic garden in Brussels in 1939. Subsequently collected in a garden in Vorst in 1954 (most likely as a weed). Subsequently seen in Mol (Den Diel) as a weed in a lawn (D’hose & De Langhe 1979; sub L. sibiricus). In 2000 also seen on a heap of soybean waste at the Ghent Grain Terminal in the port of Gent (a single specimen).
This species has long been confused with Leonurus sibiricus (Harley & Paton 2001). It has smaller corollas (9-10 mm long) and entire upper (floral) leaves (Kupryanova 1977, Shu 1994). Unlike Leonurus japonicus, L. sibiricus is a non-weedy species and all adventive records of it are most likely referable to L. japonicus.
D’hose R. & De Langhe J.-E. (1979) Nieuwe groeiplaatsen van zeldzame planten in België. VII. Bull. Soc. Roy. Bot. Belg. 112: 21-34.
Harley R. & Paton A. (2001) Leonurus japonicus Houtt. (Lamiaceae): the correct name for a common tropical weed. Kew Bull. 56: 243-244.
Kupryanova L.A. (1977) Leonurus. In: Shishkin B.K. (ed.), Flora of the U.S.S.R., vol. XXI. Academic Scienc. U.S.S.R.: 105-114.