British ferns (Filicopsida)
Sporophyte. The rhizomes stout; short, erect; bearing scales (with brown, lanceolate scales). Plants bearing markedly different fertile and sterile leaves (the linear, sorus-bearing pinnae of the fertile leaves much narrower than those of the sterile leaves).
Leaves aggregated terminally (at the ends of rhizome branches); to 15–100 cm long (to 100 x 20cm, the narrower fertile fronds scattered among the sterile ones); persistent; compound (i.e., differing from B. spicant, in that the pinnae of the sterile leaves are greatly narrowed basally and attached over only a short width); simply divided. Pinnae about 15–50 on each side of the leaf (? - numerouss). The petioles shorter than the blades (not more than a third as long as the blade and often much less); vascularised by several discrete strands. Leaf blades in outline very narrowly elliptic; somewhat leathery to herbaceous. The longest pinnae around the middle of the blade; 5–10 cm long (X 2.5 cm in sterile leaves, as long but much narrower in the fertile ones). The venation of the lamina mostly open.
The sporangia marginal to superficial (so close that the longitudinally elongated indusium could be confused with the margin); initially aggregated in sori. The sori elongated (forming continuous lines along the length of the fertile pinna, on either side of its midrib); finally becoming confluent when mature (and appearing to cover the entire underside of the pinna at maturity); with a true indusium (this first whitish, then brownish, elongated along the outside of the sorus, between it and the very narrow margin of the lamina). The mature spores monolete; without a perispore.
Distribution and habitat. In shady places and by streams. Naturalized (a South American introduction, occasionally escaping from gardens). Naturalized in southwest England, western Scotland and southwest Ireland.
Vice-county records. Britain: West Cornwall, East Cornwall, North Devon, South Somerset, Dorset, West Kent, Berkshire, Glamorgan, Cardiganshire, Argyll Main, Channel Islands. Ireland: South Kerry, North Kerry, Down.
Classification. Family Polypodiaceae (C.T.W.); Blechnaceae (Swale and Hassler); Blechnaceae (Stace). Order Athyriales (Swale and Hassler).
Special key character. The pinnae of the sterile leaves much narrowed basally, attached over only a short width.
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2004 onwards. British ferns (Filicopsida). Version: 4th January 2012. http://delta-intkey.com’.