Urtica membranacea Poiret ex Savigny (syn.: U. dubia Forssk., nom. illeg.) (Medit., Atl. Isl.) – A very rare, locally more or less persisting alien. Few plants were discovered in the city of Ghent in 2011 (De Rycke & al. 2012). Despite being regularly removed (weed killer, weeding) Urtica membranacea seems to persist well in this locality. Up to 10 or more individuals are still present in 2016. In 2013, a second locality was discovered in the same city (comm. W. Van Landuyt June 2013) but it probably not survived in this site. In 2016 also seen for the first time in Brussels (Saint-Gilles), in identical circumstances.
Urtica membranacea is a common weed in Mediterranean countries but it is unknown how it was introduced in western Europe. A potential vector of introduction might be the horticultural trade: this species has been recorded in imported containers with olive trees in garden centers (Hoste & al. 2009). Alternatively, it may have been unintentionally introduced by citizens returning from southern Europe (e.g. as seed in car mats).
Similar recent records in urban areas are known from other western European countries, for instance from the Netherlands (e.g. Beringen & al. 2015) and the British Isles (e.g. Boucher & Partridge 2006, Leslie 2009).
Selected literature:
Beringen R., Reijerse A.I. & Odé B. (2015) Zuidelijke brandnetel, een mediterrane verstekeling. Kijk op Exoten 11: 6-7. [available online at: http://www.ravon.nl/Portals/0/PDF3/Kijk%20op%20exoten_nr%2011_jan2015_we...
Boucher A. & Partridge J. (2006) Urtica membranacea, an annual nettle, in Warwick: a first British record? BSBI News 103: 29-30. [available online at: http://archive.bsbi.org.uk/BSBINews103.pdf]
Crouch H.J. (2010) Two Mediterranean weeds new to Somerset. Somerset Rare Plants Group 2010 Newsletter 11: 8-9. [available online at: http://www.somersetrareplantsgroup.org.uk/wp-content/uploads/2014/11/201...
De Rycke A., Van Landuyt W. & Hoste I. (2012) Mediterrane brandnetels in Gent: Urtica pilulifera en Urtica membranacea. Dumortiera 100: 29-32. [available online at: http://www.plantentuinmeise.be/DUMORTIERA/DUM_100/Dum%20100_29-32_Urtica...
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%...
Leslie A.C. (2009) Urtica membranacea Poiret in Cambridgeshire. BSBI News 112: 33. [available online at: http://archive.bsbi.org.uk/BSBINews112.pdf]