Centranthus ruber (L.) DC. (Medit.) – A rather rare but much increasing, locally naturalised escape from cultivation. Known since at least 1827 from rocky slopes in Namur (Citadelle, Rochers des Grands Malades). Soon afterwards discovered in many other locations in the valley of river Meuse (Dinant, Flémalle, Huy, Waulsort, Yvoir, …). More rarely also in other thermophilous valleys in Wallonia (Semois, Vesdre, …). By now widely naturalised in large parts of Wallonia, for instance around Tournai, Binche, etc. Since the 2nd half of the 19th century also known from old walls in Flanders (Lede, 1869; Leuven, 1883; Denderwindeke, 1884; …) but probably rather ephemeral for quite a long time. The naturalisation of Centranthus ruber in Flanders seems to be fairly recent. Verloove (2002) cites two well-established populations on old walls in West-Vlaanderen (Kortrijk, Nieuwpoort). In the past years further extending and by now known from numerous additional locations in Flanders, especially near the coast (climatologically more favourable): Heist, Leffinge, Stuivekenskerke, Veurne, Zwankendamme, … Furthermore recently well established on old walls in several cities, for instance in Gent and Menen. Also (sown?) on several coalmine heaps in Limburg (for instance Beringen) and subsequently becoming naturalised.
Centranthus ruber is a thermophilous species and its habitats in Belgium are always dry and sun-exposed. It mostly grows on (natural) rocky slopes, (artificial) old walls (often brick quays or concrete canal banks), more rarely on coalmine heaps or other gravelly habitats (railway yards, …).
Most plants found as an escape have pinkish or reddish corollas but white-flowered forms (cv ‘Alba’) have also been encountered in Belgium (for instance in Gent and Menen).
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Selected literature:
Geerts S., Rossenrode T., Irlich U.M. & Visser V. (2017) Emerging Ornamental Plant Invaders in Urban Areas—Centranthus ruber in Cape Town, South Africa as a Case Study. Invasive Plant Science and Management 10(4): 1-10. [available online at: https://www.researchgate.net/publication/321539665_Emerging_Ornamental_P...
Pablo Ferrer Gallego P.P. & Laguna Lumbreras E. (2013) Sobre el tipo nomenclatural de Centranthus ruber (L.) DC. (Valerianaceae). Bouteloua 16: 3-8.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Centranthus ruber. 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: 266.