Symphyotrichum subulatum (Michaux) G.L. Nesom (incl. var. squamatum (Sprengel) S.D. Sundberg, syn.: Aster squamatus (Spreng.) Hieron., Symphyotrichum squamatum (Sprengel) G. L. Nesom) (Am.) – A very rare and up to present ephemeral alien. Formerly recorded once (in 1895) as wool alien in the Vesdre valley (Verloove 2006). In 2017 a single individual was found in a worked-up roadside in Kortrijk. Although this specimen was abundantly fruiting it was no longer seen in 2018 in this area. This species is also rather frequently seen in plant nurseries where it is imported, among others, with containers with olive trees from southern Europe (Hoste & al. 2009).
Symphyotrichum subulatum is rapidly expanding in southern Europe and often considered an invasive species. It recently also reached the British Isles (e.g. Green 2007) and the Netherlands (see: http://waarneming.nl/waarneming/view/89832886). It is a bushy annual with numerous, small heads with inconspicuous ligular florets. Its re-occurrence and naturalization in Belgium in a very near future is likely.
This species was formerly known as Aster squamatus, a native from South America. According to recent insights (Brouillet & al. 2006) it is best considered part of a very variable catch-all species, Symphyotrichum subulatum. The latter includes five varieties that occur from North to South America. Only var. squamatum seems to be known from the Old World.
Selected literature
Brouillet L., Semple J.C., Allen G.A., Chambers K.L. & Sundberg S.D. (2006) Symphyotrichum. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 20. Oxford University Press, New York-Oxford: 465-539. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=132022]
Green P.R. (2007) Aster squamatus could be on its way to you. A new alien for Ireland and England. BSBI News 105: 31-32. [available online at: http://archive.bsbi.org.uk/BSBINews105.pdf]
Hoste I., Verloove F., Nagels C., Andriessen L. & Lambinon J. (2009) De adventievenflora van in België ingevoerde mediterrane containerplanten. Dumortiera 97: 1-16. [available online at: http://www.botanicgarden.be/DUMORTIERA/DUM_97/Dum%2097_1-16_Mediterrane%...
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf]