Juncus canadensis J. Gay ex Laharpe (syn.: J. longicaudatus (Engelm.) Mack.) (N-Am.) – A rare, locally naturalised xenophyte. Discovered in 1974 in the Netherlands (Reuselse Moeren), close to the Belgian frontiers (Adema 1974). Soon afterwards also found in Belgium, at first in Arendonk (D’hose 1975). A posterior herbarium revision revealed a previous record from Mol-Postel dating back to 1965 (Stieperaere 1997). Locally fast spreading after its initial introduction, especially in Belgium (perhaps less so in the Netherlands; compare Van den Bremt 2006 and Holverda & al. 2009). The invasion history of Juncus canadensis in Belgium is remarkably well documented (see for instance D’hose 1975, D’hose 1977, Smets 1980, Van Straaten 1981). More recently an isolated population was discovered in the nature reserve Gulke Putten near Wingene (Stieperaere 1997), most likely unintentionally introduced by naturalists.
Juncus canadensis is confined to natural habitats in Belgium. It grows in damp heaths, especially on the verges of slightly disturbed, more or less nitrophilous fens on acidic soils (often in nature reserves and/or other protected, vulnerable habitats) (see also Van Straaten 1981 for a detailed study of its habitat preferences in Belgium). It is a very vigorous plant and quickly forms nearly monospecific stands. Its impact on native vegetation has not been thoroughly studied so far but it clearly is an invasive species.
The exact origin of the Belgian and Dutch populations (apparently unique in Europe) remains uncertain. Juncus canadensis might have been introduced with waterfowl or with military troops.
Juncus canadensis belongs to a complex of a few, closely related taxa, the Juncus canadensis-complex (Brooks & Clemants 2000). The Belgian populations are characterised by seeds 1,2-2 mm long and obviously belong to Juncus canadensis s.str.
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Selected literature
Adema F. (1974) Juncus canadensis J. Gray ex Laharpe nieuw voor Nederland. Gorteria 7(2): 17-20.
Brooks R.E. & Clemants S.E. (2000) Juncus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 22. Oxford University Press, New York-Oxford: 211-255.
De Beer D. (1997) Juncus canadensis in het Prinsenpark te Retie. Dumortiera 68: 31.
D’hose R. (1975) Juncus canadensis J. Gay ex Laharpe, nieuw voor de Belgische flora. Bull. Soc. Roy. Bot. Belg. 108: 31-34.
D’hose R. (1977) Notities aangaande Juncus canadensis J. Gay ex Laharpe. Dumortiera 6: 35-36.
Holverda W., van Moorsel R. & Duistermaat L. (2009) Nieuwe vondsten van zeldzame planten in 2005, 2006 en ten dele 2007. Gorteria 34: 1-40.
Smets L. (1980) Canadese rus: een recente aanwinst voor de Kempense flora. De Wielewaal 43: 181-183.
Stieperaere H. (1997) Juncus canadensis en Rhynchospora fusca, onvrijwillige (her-) introductie in het Vlaams district (België). Dumortiera 67: 7-11.
Van den Bremt P. (2006b) Juncus canadensis. 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: 501-502.
Van Straaten D. (1981) Vegetaties met Juncus canadensis J. Gay ex Laharpe in de Kempen. Dumortiera 19-20: 2-11.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.