Cistus lasianthus Lam. (syn.: Halimium lasianthum (Lam.) Spach (SW Eur.) – An exceptional alien of unknown provenance. A single individual was detected under barb wire on the edge of a dry meadow in Heusden (Destelbergen), near Gent, in 2012. It was subsequently confirmed, for instance in 2014.
The species grows in a dry, sun-exposed locality on siliceous substratum, along with native species like Aira praecox, Ornithopus perpusillus, Rumex acetosella, etc. Its vector of introduction remains unknown.
The plants are characterized by petals that are entirely yellow, a character of subsp. alyssoides (Lam.) Demoly (syn.: Cistus alyssoides Lam.). This taxon, as well as cultivars of it, is frequently cultivated as an ornamental (see, e.g.: http://www.cistuspage.org.uk/Halimium%20lasianthum.htm). It was formerly accepted as a distinct species (Heywood 1968).
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Selected literature:
Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge.
Heywood V.H. (1968) Cistaceae. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 2. Cambridge University Press, Cambridge: 282-292.
Muñoz Garmendia F. & Navarro C. (1993) Cistaceae. In: Castroviejo S. & al. (eds.), Flora Iberica, vol. 3. Real Jardín Botánico, Madrid: 318-436. [available online at: http://www.floraiberica.es/PHP/familias_lista_.php?familia=Cistaceae]