Cyrtomium falcatum (L. f.) C. Presl (syn.: Polypodium falcatum L. f., Polystichum falcatum Diels) (temp. As.) – A very rare escape from cultivation, known since the late 1990’s from Zottegem. More recently also found in Antwerpen (Verloove & al. 2007). Cyrtomium falcatum grows in urban areas on basement walls or old walls. Although very persistent the species is probably not yet naturalised in Belgium.
Cyrtomium falcatum is the commonest taxon of Cyrtomium currently found as an escape in the Netherlands (Denters 2003) whereas in Belgium and the British Isles the hardier (and commercially more available) C. fortunei is the ‘usual’ escape (Edgington 2006, Verloove & al. 2007).
Cyrtomium falcatum and C. fortunei are often intermixed and erroneously identified. Their identification appears to be straightforward in Belgium although several diacritic features are perhaps of little value. The very tough (Ilex-like!), glossy fronds of Cyrtomium falcatum are very diagnostic but this character becomes much less noticeable when pressed. The margins of the fronds are wavy with a remarkably involute, pale cartilagineous, entire border whereas in Cyrtomium fortunei the margins are much less involute, with a narrower pale border and irregularly but prominently toothed (at least distally). As a rule Cyrtomium falcatum plants have less pinnae per frond (at least in Belgium; this does not always apply to well-developed plants in warmer areas) and pinnae are often wider and more oblique at base.
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Selected literature
Bonafede F., Ferrari C. & Vigarani A. (1993) Cyrtomium falcatum, new to the Italian flora. Flora Mediterranea 3: 261-264.
Denters T. (2003) Verleden en heden van Ijzervaren (Cyrtomium falcatum (L.f.) C.B. Presl.) in Nederland. Gorteria 29: 125-133.
Edgington J.A. (2006) Wall-to-wall ferns. BSBI News 102: 20-21.
Parrot A.G. (1982) Une fougère exotique: Polystichum falcatum Dils., var. rochefordii, naturalisée à Biarritz, 64200, France. Bull. Soc. Bot. Centre-Ouest, N.S. 13: 15-23.
Röhner G. (2012) Angesalbte und adventive Farnpflanzen an der Bergstrasse. Hess. Florist. Br. 60(2): 20-24.
Verloove F., van der Ham R. & Denters T. (2007) Exotische muurvarens in België en Nederland. Dumortiera 92: 1-16.