Gamochaeta pensylvanica (Willd.) Cabrera (syn.: Gnaphalium pensylvanicum Willd., G. spathulatum Lam., G. peregrinum Fernald) (Am.) – A very rare alien. Recorded as a weed in a greenhouse in 1891 near Liège. Discovered in 2007 as an urban weed in Wilrijk (foot of wall). Its presence there was subsequently confirmed on several occasions (2008, 2014) and by now (2018) it can be considered locally naturalized (comm. D. De Beer). Similar but much more numerous records are available from several cities in the Netherlands (Amsterdam, Nijmegen, Utrecht, etc.). These were initially wrongly ascribed to Gamochaeta purpurea (L.) Cabrera (syn.: Gnaphalium purpureum L.) (Holverda & al. 2009), possibly following Stace (2010). Gnaphalium pensylvanicum is a recently increasing alien in parts of (southern) Europe and is apparently mostly introduced via nurseries, for instance with imported Olea containers (Hoste & al. 2009). As a result, it is also regularly seen as a garden weed, e.g. in Bellem, Pulle, etc.
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Selected literature:
Atha D., Alvarez R., Feeser D., Feder M., Wang Z, & Kelly R. (2016) Gamochaeta pensylvanica (Asteraceae) is established in the New York flora. Phytoneuron 2016-22: 1–4. [available online at: http://www.phytoneuron.net/2016Phytoneuron/22PhytoN-NYGamochaeta.pdf]
Carretero J.L. & Esteras F.J. (1979) Sobre la presencia de Gamochaeta pensylvanica (Willd.) Cabrera en España. An. Inst Bot. A.J. Cavanilles 36: 407. [available online at: http://dialnet.unirioja.es/servlet/articulo?codigo=3010301]
Danin A. (2000) The Nomenclature News of Flora Palaestina. Flora Mediterranea 10: 109-172. [available online at: http://147.163.105.223/flora/10-109.pdf]
Feder J. (2012) Pennsylvanisches Ruhrkraut Gnaphalium pensylvanicum Willd. erstmals in Nordwestdeutschland. Bremer Botanische Briefe 16: 2-3. [available online at: http://www.internetchemie.info/botanik/bbb/bremer-botanische-briefe-16.pdf]
Holverda W., van Moorsel R. & Duistermaat L. (2009) Nieuwe vondsten van zeldzame planten in 2005, 2006 en ten dele 2007. Gorteria 34: 1-40.
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%20containerplanten_Hoste%20et%20al.pdf]
Latham J.B. (1984) Two notable escapees. BSBI News 38: 20-23. [available online at: http://archive.bsbi.org.uk/BSBINews38.pdf]
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.