9. Geranium pyrenaicum Burm. f. (Eur., SW-As., N-Afr.) – A rather frequent, more or less widely naturalised alien. Known at least since 1824 (Durand 1899) but Geranium pyrenaicum long remained local and rare in Belgium. Its spread and naturalisation seem to date back to the first half of the 20th century (Verloove 2002). At present it is fairly common in large parts of Wallonia (mainly on calcareous substrates) and Flanders. In Flanders Geranium pyrenaicum is remarkably centred around Brussel, the valley of river Maas, on loamy soil in the southern part of Limburg and in the westernmost coastal areas. Geranium pyrenaicum is most often found in roadverges, canal banks, by railway tracks,… It usually grows in rather damp and nitrophilous habitats. It easily competes with native species without displaying invasive tendencies (Verloove 2002).
Geranium pyrenaicum is usually readily identified but large-flowered forms of native G. molle are often much alike. However, the latter clearly is an annual and its mericarps are always glabrous. Geranium brutium, likely to have been overlooked in Belgium (see introduction and Sell & Murrell 2009), shares the large petals with G. pyrenaicum but has glabrous mericarps and petals with a distinct claw. Petals are usually bright pink in Geranium pyrenaicum but entire populations with pale pink (nearly whitish) petals exist (for instance on the east bank of the Voorhaven in the port of Gent).
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Selected literature:
Allemeersch L. (2006) Geranium pyrenaicum. 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: 438-439.
Durand T. (1899) Phanérogames. In: De Wildeman E. & Durand T., Prodrome de la flore belge. A. Castaigne Editeur, Bruxelles: 1112 p.
Sell P. & Murrell G. (2009) Flora of Great Britain and Ireland. Vol. 3 Mimosaceae – Lentibulariaceae. Cambridge University Press, Cambridge: XXVIII + 595 p.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.