British ferns (Filicopsida)
Athyrium alpestre Rylands ex T. Moore, Polypodium alpestre (Hoppe) Spenn. Including A. flexile (Newman) Druce.
Sporophyte. The rhizomes stout; short, more or less erect; bearing scales (these large, lanceolate, soft, and brown).
Leaves aggregated terminally; to 20–30(–75) cm long; complexly divided; bipinnate with conspicuously divided pinnules (almost tripinnate, the pinnules more or less contiguous, pinnately lobed to pinnatifid). Pinnae 12–25 on each side of the leaf (?). Leaves not conspicuously bent near the junction of rachis and petiole. The petioles shorter than the blades (scaly at least below, with lanceolate, brown scales which are relatively shorter than in A. filix-femina); about 0.2–0.3 x the length of the blade (about a quarter as long, pale yellow-green, almost translucent, often basally pinkish or straw-coloured); 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 lanceolate (tapered fairly abruptly to an acuminate apex); not covered underneath with rust-coloured scales. The longest pinnae around the middle of the blade; 3–25 cm long. The pinnae decreasing markedly in length towards the base of the blade, the basal ones relatively short (the lower pinnae opposite and remote). 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 approximated but not strongly overlapping (in the upper part of the leaf), or distant from one another and not at all overlapping (in the lower part). The venation of the lamina open.
The sporangia superficial; exposed; aggregated in sori. The sori commoner near the base 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 indusia falling long before the spores are ripe). The mature spores with a perispore.
Distribution and habitat. On neutral substrates to on acid substrates. Calcifuge, in acid gullies, boulder slopes and scree, rarely below 600 m. In central and northern Scotland, sometimes with A. filix-femina, local.
Vice-county records. Britain: Roxburghshire, Stirlingshire, West Perthshire, Mid Perthshire, East Perthshire, Angus, South Aberdeenshire, Banffshire, East Inverness-shire, West Inverness-shire, Argyll Main, Dunbartonshire, West Ross, East Ross, East Sutherland, West Sutherland, Caithness.
Classification. Family Polypodiaceae (C.T.W.); Athyriaceae (Swale and Hassler); Woodsiaceae (Stace). Order Athyriales (Swale and Hassler).
Illustrations. • A. distentifolium: as A. eu-alpestre, Eng. Bot. 1870 (1886). • A. distentifolium: Sowerby and Johnson (1859). • Athyrium distentifolium and A. filix-femina (inter alia).
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’.