The familial circumscription of Woodsiaceae dramatically changed in recent years, mostly as a result of molecular phylogenetic studies (see e.g. Smith & al. 2006, Schuettpelz & al. 2016 for an overview). Compared with the latest edition of the Belgian flora (Lambinon & Verloove 2012) Matteucia and Onoclea – both genera with highly dissimilar fertile and sterile leaves – have been removed and are now accommodated in Onocleaceae. The other native genera (Athyrium, Cystopteris and Gymnocarpium) remained in Woodsiaceae (Smith & al. 2006). Additional studies, however, suggest further changes (Schuettpelz & al. 2016): Woodsiaceae is reserved for Woodsia only while Athyrium is accommodated in Athyriaceae and Cystopteris and Gymnocarpium in Cystopteridaceae. A more conservative approach is followed in this account.
1. Rhizomes long-creeping with fronds appearing singly. Indusium absent (native) === Gymnocarpium
1. Rhizomes short with fronds appearing in tufts. Indusium present === 2
2. Indusium attached laterally, flap like and persistent === Athyrium
2. Indusium attached at proximal side of sorophore, early deciduous (native) === Cystopteris
Literature
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Schuettpelz E. & al. (2016) A community-derived classification for extant lycophytes and ferns. Journ. Syst. Evolut. 54(6): 563-603. [available online at: https://arizona.pure.elsevier.com/en/publications/a-community-derived-cl...
Smith A.R., Pryer K.M., Schuettpelz E., Korall P., Schneider H. & Wolf P.G. (2006) A classification for extant ferns. Taxon 55(3): 705-731. [available online at: https://www.fieldmuseum.org/sites/alienplantsbelgium.bedefault/files/smi...