Cymbalaria muralis P. Gaertn., B. Mey. et Scherb. (syn.: Linaria muralis (L.) Miller) (SC Eur.) – A rather commonly naturalized escape from cultivation. Already known in the second half of the 16th century (Van Landuyt 2006). Its expansion, however, is fairly recent (van Rompaey & Delvosalle 1978, Verloove 2002). At present it has become, along with Asplenium ruta-muraria, one of the most widespread and characteristic wall plants in large parts of Belgium. From its secondary distribution range, the Cymbalarietum muralis association has been described, a pioneer community of vertical wall surfaces (e.g. Szczęśniak & Świerkosz 2003).
Although mostly restricted to highly artificial habitats (i.e., walls in urban areas) Cymbalaria muralis is sometimes considered an invasive species or undesirable weed, for instance in Japan (http://www.nies.go.jp/biodiversity/invasive/DB/detail/81470e.html). Its seeds are transported by ants and easily germinate in cracks and fissures. Once established plants are hard to eradicate and become weedy. These days, Cymbalaria muralis is more of a weed rather than a garden ornamental in Belgium.
Cymbalaria muralis is a variable species. The naturalized taxon is glabrous at maturity and belongs to subsp. muralis. A persistently pubescent variant with long pedicels was recorded once in 1900 (subsp. pubescens (C. Presl) D.A. Webb; see Verloove 2006). A peculiar variant with deeply incised leaves is sometimes distinguished as f. toutonii (A. Chev.) Cuf. (syn.: C. toutonii A. Chev.) and was recorded in 2011 in gravel in Queue-du-Bois (see also McClintock 1982, Coombe 1992). Finally, a white-flowered form has also been recorded (cv ‘Alba’). Some of these variants have been given species rank (see for instance Lattanzi & Leporatti 1980, Bigazzi & Raffaelli 2000).
Selected literature:
Bigazzi M. & Raffaelli M. (2000) Taxonomy of two Cymbalaria species (Scrophulariaceae) endemic to Italy: C. glutinosa sp. nov. and C. pubescens (J. and C. Presl) Cuf. Webbia 54(2): 193-205.
Coombe D.E. (1992) Cymbalaria muralis forma toutonii. B.S.B.I. News 60: 62. [available online at: http://archive.bsbi.org.uk/BSBINews60.pdf]
Dane F. & Olgun G. (1989) A new record for the flora of European Turkey: Cymbalaria muralis subsp. muralis. Istanbul Univ. Ecz. Fak. Mecm. 25: 37-39.
Feder J. (2002) Das Mauer-Zimbelkraut (Cymbalaria muralis P. GAERTN., B. MEY & SCHREB.) in Ostfriesland. Beiträge zur Vogel- und Insektenwelt Ostfrieslands 186: 10.
Junghans T. (2003) Untersuchungen zur Besiedlung von Mauern durch
Cymbalaria muralis. Braunschweig. [available online at: http://www.ruderal-vegetation.de/epub/cymbalar.pdf]
Junghans T. (2004) Zur Diasporenausbreitung von Cymbalaria muralis (Scrophulariaceae).
Braunschweig: 19 p. [available online at: http://digisrv-1.biblio.etc.tu-bs.de:8080/docportal/receive/DocPortal_document_00001637]
Junghans T. (2008) Aspects of dispersal in Cymbalaria muralis (Scrophulariaceae). Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 127(3): 289-298. [available online at: http://www.schweizerbart.de/papers/pde/detail/127/52904/Aspects_of_dispersal_in_Cymbalaria_muralis_Scrophulariaceae]
Lattanzi E. & Leporatti G.M.L. (1980) Sulla distribuzione nel Lazio di Cymbalaria pilosa (Jacq.) L. Bailey e di Cymbalaria muralis Gaertner, Meyer & Scherb ssp. visianii D.A. Webb. Ann. Bot. (Italy) 38(1-2): 103-105.
Leporatti M.L., Del Caldo L. & Pavesi A. (1994) Confronto tra Cymbalaria muralis Gaertn., Mey., et Scherb. subsp. muralis e C. muralis subsp. visiani D.A. Webb osservazioni sulla anatomia, morfologia e distribuzione in Italia. Ann. Bot. (Rome) 52 suppl. 2: 479-488.
McClintock D.A. (1982) The story of Cymbalaria toutonii A. Chev. Watsonia 14: 182-183. [available online at: http://archive.bsbi.org.uk/Wats14p177.pdf]
Oberdorfer E. (1969) Zur Soziologie der Cymbalaria-Parietarietea, am Beispiel der Mauerteppich-Gesellschaften Italiens. Vegetatio 17: 208-213.
Szczęśniak E. & Świerkosz K. (2003) Cymbalaria muralis P. Gaertn., B. Mey. & Schreb.and
Cymbalarietum muralis Görs 1966 in Lower Silesia - expansion or regression? In: Phytogeographical problems of synanthropic plants: 185-193. [available online at: http://www.academia.edu/2281509/Cymbalaria_muralis_L._and_Cymbalarietum_muralis_Gors_66_in_Lower_Silesia_exctincion_or_regresion]
Truchan M. (2006) Distribution of Cymbalaria muralis P. Gaertn., B. Mey. & Scherz. in the central part of Polish Pomerania. Biodiversity: research and conservation 1-2: 98-101.
Van Landuyt W. (2006) Cymbalaria muralis. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 322-323.
Van Rompaey E. & Delvosalle L. (1978) Atlas de la flore belge et luxembourgeoise. Ptéridophytes et Spermatophytes. Commentaires. Jardin Botanique National de Belgique, Meise: 116 p.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p.
Watt H.B. (1956) Notes on the introduction and distribution of Cymbalaria muralis Gaertn. Mey. & Scherb. in Scotland. Bot. Soc. Brit. Isles Proc. 2: 123-125.