British ferns (Filicopsida)
Sporophyte. The rhizomes short, creeping to erect; bearing scales (the scales dark, narrow). Plants with no clear distinction into fertile and sterile leaves.
Leaves aggregated terminally; to 5–15(–20) cm long; persistent to dying in the autumn (less persistent than in A. trichomanes); circinnate; compound; simply divided, or simply divided to complexly divided (the pinnae crenate or crenate-dentate distally); if more or less complexly divided, once pinnate, with conspicuously divided pinnae. Pinnae 15–40 on each side of the leaf. The petioles shorter than the blades to about as long as the blades (relatively longer than in A. trichomanes, brownish or blackish only near the base and green above, wingless or very narrowly green-winged); vascularised via a single strand (representing fusion of a pair of leaf traces). The petioles brownish or blackish only near the base and green above, the rachides green and either wingless or at most only narrowly green-winged. Leaf blades in outline linear; herbaceous (not leathery). The longest pinnae around the middle of the blade (the pinnae more or less equal in length for some distance around the middle, and less diminution towards the base than in A. trichomanes); 3–7(–10) cm long. The venation of the lamina open.
The sporangia superficial; protected; aggregated in sori. The sori linear elongated (several borne obliquely on either side of the pinna, nearer its midrib than the margin, situated mainly below the fork of the veins, but sometimes extending along the upper fork); remaining discrete at maturity; with a true indusium. The indusia attached on one side along a vein. Paraphyses absent. The mature spores monolete; with a perispore.
Distribution and habitat. On base-rich substrates. Base-rich, mainly limestone rock crevices. Eastern and northern Britain to south to S Wales and Derbyshire (and formerly Warwickshire), local.
Vice-county records. Britain: West Sussex, Surrey, Middlesex, Monmouthshire, Herefordshire, Worcestershire, Warwickshire, Staffordshire, Glamorgan, Breconshire, Radnorshire, Carmarthenshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Denbighshire, North Lincolnshire, Leicestershire, Derbyshire, South Lancashire, West Lancashire, North-east Yorkshire, South-west Yorkshire, Mid-west Yorkshire, North-west Yorkshire, Durham, South Northumberland, North Northumberland, Westmorland, Cumberland, Dumfriesshire, Kirkcudbrightshire, Ayrshire, Renfrewshire, Lanarkshire, Peeblesshire, Selkirkshire, Roxburghshire, Midlothian, Fifeshire, Stirlingshire, West Perthshire, Mid Perthshire, East Perthshire, Angus, South Aberdeenshire, North Aberdeenshire, Banffshire, Moray, East Inverness-shire, West Inverness-shire, Argyll Main, Dunbartonshire, Clyde Isles, Kintyre, South Ebudes, Mid Ebudes, North Ebudes, West Ross, East Ross, East Sutherland, West Sutherland, Caithness, Outer Hebrides, Shetland. Ireland: South Kerry, North Kerry, West Cork, Mid Cork, Waterford, South Tipperary, Limerick, West Galway, West Mayo, Sligo, Leitrim, Fermanagh, East Donegal, West Donegal, Down, Antrim, Londonderry.
Classification. Family Polypodiaceae (C.T.W.); Aspleniaceae (Swale and Hassler); Aspleniaceae (Stace). Order Aspleniales (Swale and Hassler).
Illustrations. • A. viride: Eng. Bot. 1877 (1886). • A. viride: Sowerby and Johnson (1859). • 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’.