British ferns (Filicopsida)
= Athyrium distentifolium var. flexile (Newman) Jermy.
Sporophyte. The rhizomes stout; short, more or less erect; bearing scales (these large, lanceolate, soft, and brown).
Leaves aggregated terminally (spreading); to (10–)20–35 cm long; compound; complexly divided; bipinnate with more or less undivided pinnules, or bipinnate with conspicuously divided pinnules (the pinnules well separated, coarsely toothed to pinnatifid). Pinnae 12–30 on each side of the leaf (?). Leaves conspicuously bent near the junction of rachis and petiole (bent at or just above the base of the blade, sometimes flexuous). The petioles shorter than the blades (scaly at least below); about 0.1–0.2 x the length of the blade (only up to a fifth as long, yellow-green or reddish); vascularised via a single strand (this gutter-shaped, representing either a single leaf trace arising from the lower angle of the leaf gap, or fusion of a pair?). Leaf blades in outline narrowly oblong to elliptic (tapered gradually to an acute apex). The longest pinnae around the middle of the blade; 2–20 cm long (?). The pinnae decreasing markedly in length towards the base of the blade, the basal ones relatively short to not decreasing markedly in length basipetaly, the basal pinnae not or scarcely shorter than the longest pair (i.e., less markedly decrescent than in A. filix-femina and A. distentifolium, and further differing from them in that the lower deries of pinnae are alternate, contiguous and and sometimes more obviously deflexed). The lowest pinna with the basal pinnule on its lower side nearly always less than half as long as the pinna itself. The adjacent pinnae tending to be distant from one another and not at all overlapping. The venation of the lamina open.
The sporangia superficial; exposed; aggregated in sori. The sori commoner near the apex of the blade, sub-orbicular (very small, each on a receptacle with a vascular strand from the vein, borne one per pinnule segment in rows down either side of the pinnule, nearer its margin than its midrib); remaining discrete at maturity; initially with a true indusium, or naked and neither indusiate nor pseudo-indusiate (when mature, the indusium falling long before the spores are ripe). The mature spores with a perispore.
Distribution and habitat. On acid substrates. In damp acid rocky places, at 1040–1140m. Very local, in central Scotland, often found with A. distentifolium.
Vice-county records. Britain: Mid Perthshire, Angus, South Aberdeenshire, Banffshire, East Inverness-shire, West Inverness-shire, Argyll Main.
Classification. Family Polypodiaceae (C.T.W.); Athyriaceae (Swale and Hassler); Woodsiaceae (Stace). Order Athyriales (Swale and Hassler).
Comments. See Jermy, A.C. and McHaffie (1998).
Illustrations. • A. flexile: as A. alpestre var. flexile, Eng. Bot. 1871 (1886).
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’.