2. Tsuga heterophylla (Rafin.) Sarg. (syn.: T. albertiana (A. Murray) Sénécl.) (W-N Am.) – A very rare escape from cultivation but possibly overlooked. Recorded from 2008 onwards at various locations throughout Flanders: in an abandoned arboretum in Koekelare (along with Tsuga canadensis), Sterrebos near Roeselare, in a nature reserve in Zoersel (Zoerselbos) and doubtlessly elsewhere.
1. Ailanthus altissima (Mill.) Swingle (syn.: A. glandulosa Desf., Toxicodendron altissimum Mill.) (China) – A frequently cultivated ornamental tree, in private gardens and even more so in public parks and old estates. The history of the escape of Ailanthus altissima in Belgium is rather well documented. Its naturalisation apparently started in natural habitats in some thermophilous river valleys in Wallonia. It was first reported as being naturalised from sun-exposed rocky slopes in the valley of river Meuse near Huy in 1952 (old vineyard).
Recent molecular phylogenetic research strongly suggests the inclusion of Chenopodiaceae in Amaranthaceae (APG 1998-2009). This taxonomy became widely accepted in recent times (see for instance van der Meijden 2005, Stace 2010) and is adopted here as well.
Leycesteria formosa Wallich (Himalayas) – A very rare but increasing, locally naturalizing escape from cultivation. First collected in Tournai (foot of wall in urban environment) in 2006. Recorded in abundance on walls and as a weed on the Campo Santo cemetery in Gent in 2007. Also seen at the foot of a hedge in the city of Kortrijk in 2008 and on a quay wall in Brugge in 2012. A very large, obviously naturalized population was discovered on a woody talus slope of motorway E17 in Kortrijk in 2013.
Vincetoxicum rossicum (Kleopow) Barbar. (syn.: Antitoxicum rossicum (Kleopow) Pobed., Cynanchum rossicum (Kleopow) Borhidi) (former USSR) – An exceptional alien, recorded only once in Wechelderzande in 1965, without obvious vector of introduction (probably an escape from cultivation; see also Markgraf 1971).
Hedera colchica (K. Koch) K. Koch (Caucasus) – A rare but increasing escape from cultivation or garden throw-out. Apparently first documented as an escape from Groenendaal (Hoeilaart) in 1952. Already reported as naturalised in Lambermont in 1955 but obviously long overlooked elsewhere. Increasingly recorded since 2005 and at present known from several, widely scattered locations, for instance in Angleur (Sart Tilman), Bellem (Aalter), Diksmuide and Kortrijk.
Artemisia austriaca Jacq. (E and C-Eur., As.) – A very rare, formerly locally naturalised alien, possibly a garden escape. Discovered in 1944 in Braine l’Alleud (Sart Moulin) along a talus slope close to the railway station (on a stony, dry, sun-exposed site). Subsequently extending to nearby old walls and wasteland. This population was last confirmed in 1957 and probably little later destroyed as a result of infrastructural works.
An updated MS-Excel spreadsheet version of the checklist
Malva pseudolavatera Webb et Berthelot (syn.: M. linnaei F. Ray, M. multiflora (Cav.) Soldano, Banfi et Galasso, Lavatera cretica L.) (Medit., Macaronesia, W-Eur.) – A rare and ephemeral alien but possibly insufficiently known and overlooked. First recorded in 1997 in the port of Gent and subsequently in the port of Roeselare, Antwerpen (Merksem) and Leuven.