Adiantum raddianum C. Presl (syn.: A. cuneatum Langsd. et Fisch.) (trop. Afr., trop. Am.) – A rare escape from cultivation, increasingly found since 2003 in some larger cities (Antwerpen, Brussel and Gent), occasionally elsewhere (for instance in Kontich since 2008). Single plants are usually found on basement walls, more rarely also on damp, north-facing walls (for instance against rain pipes) or on foot of walls. Temporarily persistent in some of its locations, on a basement wall in Heverlee at least since 2003. Also a common weed in greenhouses.
Recently also reported from some neighboring countries (Germany, the British Isles, the Netherlands).
According to Keil & al. (2009) Adiantum raddianum should be regarded as a collective species (with different chromosome numbers). Assessing the exact identity of plants currently found as an escape therefore possibly requires further research. Recent molecular studies have shown that the A. raddianum group consists of 17 species; the entire complex is strongly supported as monophyletic (Hirai & al. 2016).
Literature
Crouch H.J. (2008) Adiantum raddianum – not a new vice-county record for North Somerset (v.c. 6). BSBI News 109: 52.
Dickoré W.B., Lewejohann K. & Urner R. (2009) Neufunde, Bestätigungen und Verluste in der Flora von Göttingen (Süd-Niedersachsen). Florist. Rundbriefe 42: 5-59.
Dierkes A.-H., Sarazin A., Fuchs R., Loos G.H. & Keil P. (2005) Ein Vorkommen von Adiantum raddianum C. Presl (Adiantaceae) in Essen (Nordrhein-Westfalen). Flor. Rundbr. 39: 45-49.
Edgington J.A. (2005) Exotic ferns on London walls. BSBI News 100: 42-44.
Hirai R.Y., Schuettpelz E., Huiet L., Pryer K.M., Smith A.R. & Prado J. (2016) Phylogeny and relationships of the neotropical Adiantum raddianum group (Pteridaceae). Taxon 65(6): 1225-1235. [available online at: http://pryerlab.biology.duke.edu/uploads/media_items/hirai-et-al-2016-ph...
Keil P., Sarazin A., Fuchs R. & Riedel C. (2009) Pteris cretica und Adiantum raddianum (Pteridophyta) in Licht- und Brunnenschächten im Ruhrgebiet – breiten sich subtropische Farnarten in Deutschland aus? Kochia 4: 135-146.
Rumsey J. (1998) Adiantum raddianum Presl in London. BSBI News 78: 60.
Van der Ham R. & Verloove F. (2002) Venusharen in België en Nederland. Gorteria 28: 139-141.