Agastache rugosa (Fisch. et C.A. Mey.) O. Kuntze (E-As.) – A very rare but increasing escape from cultivation, so far always ephemeral. Apparently first recorded on a landfill along river Mandel in Emelgem in 2007, along with numerous other garden plants. Also seen on ground heaps at the railway station in Veurne in 2008 and as a garden weed in Bellem in 2009. Recent records are available from, for instance, Gent and Leuven as well.
Agastache rugosa is now increasingly planted in pots in urban areas (incl. prairie gardens). It abundantly self-seeds and will surely occur as an escape elsewhere in Belgium. Identical records of Agastache rugosa are available from neighbouring countries (Clement 2005, Verloove 2008).
Agastache rugosa is by far the commonest species of the genus in cultivation. However, it is rather variable in corolla dimensions and large-flowered plants (like those from Bellem) are easily mistaken for Agastache urticifolia (Benth.) O. Kuntze.
Selected literature:
Clement E.J. (2005) Agastache rugosa - an alien new to Britain. BSBI News 99: 46-47.
Pliszko A. (2015) Agastache Rugosa (Lamiaceae), A New Casual Alien In The Flora Of Poland. Botanica Lithuanica 21(1): 74-76. [available online at: https://www.researchgate.net/publication/280937737_Agastache_Rugosa_%28Lamiaceae%29_A_New_Casual_Alien_In_The_Flora_Of_Poland]
Verloove F. (2008) La flore urbaine de Dunkerque (Nord): quelques xénophytes remarquables. Le Monde des Plantes 494: 11-14.