Equisetum scirpoides Michx. (N Euras., N Am.) – An exceptional and probably ephemeral alien of unknown provenance (see below). Discovered in 2007 in the Buitengoor nature reserve in Mol and subsequently confirmed during several years. However, no longer seen in 2014 (comm. R. Barendse). In Mol Equisetum scirpoides was found on damp, open sandy ground, in circumstances that roughly correspond with its native habitat. The fact that its nearest native populations are located in Scandinavia, more than 1000 kilometers to the north, suggests an introduction.
The origin of this species in Mol is unknown. Theoretically, Equisetum scirpoides may have been introduced by migrating waterfowl. A recently detected, relatively isolated locality in Pennsylvania in North America, was considered native (Tracey & Woods 2012). Another possibility is that it should be considered an escape from cultivation or a mere throw-out, the species being cultivated as an ornamental (e.g. Page & Bennell 1986, Jäger & al. 2008). Finally, a deliberate introduction cannot be ruled out. Several other species, including Pinguicula vulgaris (Slembrouck 2009), have been introduced on purpose in this nature reserve.
In the Buitengoor nature reserve Equisetum scirpoides was initially identified as the rare native species E. variegatum. Both are morphologically very similar but readily distinguished on characters provided in the key. However, claims of E. variegatum outside of its known indigenous distribution in Belgium (at present only in coastal areas near to De Panne) are potentially suspected and could also be referable to E. scirpoides (although both seem to be available in horticulture).
Hauke R.L. (1963) A taxonomic monograph of Equisetum subgenus Hippochaete. Beih. Nova Hedwigia 8: 1-123.
Hauke R.L. (1993) Equisetaceae. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 2. Oxford University Press, New York-Oxford: 76-84. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=111897]
Igarashi H. (2004) Distribution of Equisetum scirpoides and E. variegatum in Hokkaido, northern Japan (in Japanese). J. Jap. Bot. 79(5): 334-338.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Jones M.T. & Patterson W.A. (2011) Environmental Factors Influencing the Local Abundance of Equisetum scirpoides Near the Southern Extent of Its Range. Rhodora 113(954): 187-200.
Malme L. (1974) Equisetum scirpoides found at Hustadvika, west Norway (in Norwegian). Blyttia 32(2): 119-122.
Øllgaard B. (2000) Equisetaceae. In: Jonsell B. (ed.), Flora Nordica, vol. 1. The Bergius Foundation, Stockholm: 17-27.
Page C.N. & Bennell F.M. (1986) Equisetum. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 1: 5-6. Cambridge University Press, Cambridge.
Slembrouck J. (2009) Pinguicula vulgaris (vetblad) uitgeplant in het Buitengoor (Mol, prov. Antwerpen). Dumortiera 97: 26-27. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_97/Dum%2097_26-27_Pinguicula%20vulgaris_Slembrouck.pdf]
Tracey C. & Woods P.G. (2012) A New Native Plant for Pennsylvania, Equisetum scirpoides Michx. (Equisetaceae). Rhodora 114(960): 406-408. [available online at: https://www.researchgate.net/publication/259332063_A_New_Native_Plant_for_Pennsylvania_Equisetum_scirpoides_Michx._%28Equisetaceae%29