British ferns (Filicopsida)
Sporophyte. The rhizomes short, creeping; bearing scales (when young, the scales dark, subulate).
Leaves aggregated terminally; to 4–15 cm long; persistent; simple; more or less dichotomously divided and 1–2(-3) times forked, the stalked forks often unequal, the segments linear-cuneiform. The petioles about as long as the blades (rarely), or longer than the blades (usually several times as long, their bases blackish, the rest dull green like the rachis and the rest of the leaf, with a few small hairs when young); vascularised via a single strand (representing fusion of a pair of leaf traces). The venation of the lamina open.
The sporangia superficial; ambiguously aggregated in sori. The sori narrowly linear elongated (5–20 mm long, covering almost the whole surface and length of the segment); with a true indusium. The indusia attached on one side along a vein; whitish, entire. The mature spores monolete; with a perispore.
Distribution and habitat. On acid substrates. In rock crevices in acid places, mainly upland. Very local, in western and northern Britain from S Devon to W Ross, also in W Galway.
Vice-county records. Britain: South Devon, North Devon, South Somerset, East Kent, Surrey, Radnorshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Mid-west Yorkshire, Durham, South Northumberland, North Northumberland, Westmorland, Cumberland, Peeblesshire, Roxburghshire, Midlothian, Fifeshire, East Perthshire, South Aberdeenshire, East Inverness-shire, West Inverness-shire, North Ebudes, West Ross, East Ross, West Sutherland. Ireland: West Galway, Down.
Classification. Family Polypodiaceae (C.T.W.); Aspleniaceae (Swale and Hassler); Aspleniaceae (Stace). Order Aspleniales (Swale and Hassler).
A. x alternifolium Wulfen = A. trichomanes x A. septentrionale; A. x murbeckii Dörfl. = A. ruta-muraria x A. septentrionale.
Illustrations. • A. septentrionale: Eng. Bot. 1882 (1886). • A. septentrionale: Sowerby and Johnson (1859). • A. x alternifolium (A. septentrionale x A. trichomanes): as A. germanicum, Eng. Bot. 1881 (1886). • 9 British Aspleniaceae (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’.