Dryopteris is a large genus of ca. 250 species. Most are native in temperate Asia. Six species are native in Belgium as well: Dryopteris affinis (Lowe) Fraser-Jenkins, D. carthusiana (Vill.) H.P. Fuchs, D. cristata (L.) A. Gray, D. dilatata (Hoffmann) A. Gray, D. expansa (C. Presl) Fraser-Jenkins et Jermy and D. filix-mas (L.) Schott. Most grow naturally in woodlands but some are increasingly found in urban, man-made habitats as well, especially in Flanders (brick quays, basement walls, in sewers, etc.). In recently planted woodlands species of Dryopteris (and Polystichum) are increasingly recorded, also in areas where they were not known historically. One of the species concerned is D. affinis (with at least two subspecies: subsp. borreri (Newman) Fraser-Jenkins and subsp. affinis). It is unclear whether or not these records reflect a natural range extension or are the result of plants escaping from ornamental plantings.
In addition to the two exotic species included in this account many other taxa of Dryopteris are in cultivation (native as well as non-native). Page & Bennell (1986) enumerate 11 species for Europe and Joe Hoshizaki & Wilson (1999) even 50 for the United States. In the Netherlands several have been recorded in the wild recently: Dryopteris dickinsii (Franch. & Sav.) C. Chr. and D. wallichiana (Spreng.) Hyl. (see: www.waarneming.nl). Out of these, the latter perhaps is the least rare. It resembles native D. affinis a lot but its leaves are even more leathery and the petiole scales are still darker (at least with age), and long and narrow.
Cultivars of native species, especially of Dryopteris filix-mas (L.) Schott, are also frequent in cultivation. Forms with cristate leaves (cv ‘Cristata’) were recently introduced along a former railway track near Zonhoven (nature reserve De Teut). A form with laciniate leaves (cv ‘Linearis’) has been recorded from a basement wall in the city of Antwerpen in 2005 and in 2015 a peculiar cultivar (cv ‘Linearis-Polydactyla’) was seen in recently planted woodland near Roeselare.
1 Young fronds and indusia coppery-pink, broadly triangular in outline (definitely widest at base) === Dryopteris erythrosora
Young fronds green, lanceolate to triangular in outline, indusia never reddish-pink === 2
2 Fronds 1-pinnate, thin-leathery. One introduced species in urban areas === D. cycadina
Fronds 2-4-pinnate, herbaceous, less often leathery. Native species of woodlands, fens or old walls, some species also in urban areas === D. affinis, D. carthusiana, D. cristata, D. dilatata, D. expansa and D. filix-mas
Edgington J.A. (2003) Ferns of the metropolis – a status report. Lond. Nat. 82: 59-73.
Fraser-Jenkins C.R. (1986) A classification of the genus Dryopteris (Pteridophyta: Dryopteridaceae). Bull. Br. Mus. Nat. Hist. (Bot.) 14: 183-218.
Fraser-Jenkins C.R. (1989) A monograph of Dryopteris (Pteridophyta: Dryopteridaceae) in the Indian subcontinent. Bull. Br. Mus. Nat. Hist. (Bot.) 18: 323-477.
Guillot Ortiz D., Mateo Sanz G. & Rosselló Picornell A. (2006) Claves para la pteridoflora ornamental de la Comunidad Valenciana. Bouteloua 1: 25-33. [available online at: https://www.researchgate.net/publication/28136533_Claves_para_la_pterido...
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.
Joe B. (1963) Species of Dryopteris cultivated in California. Baileya 11: 117-130.
Joe Hoshizaki B. & Wilson K.A. (1999) The cultivated species of the fern genus Dryopteris in the United States. American Fern Journal 89: 1-98. [available online at: http://www.biodiversitylibrary.org/item/100122#page/1/mode/1up]
Page C.N. & Bennell F.M. (1986) Dryopteris. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 1: 54-57. Cambridge University Press, Cambridge.