British ferns (Filicopsida)
Sporophyte. The rhizomes creeping; bearing scales (densely covered with brown scales). Plants with no clear distinction into fertile and sterile leaves.
Leaves distributed along the rhizomes (but close together); to 15–30(–45) cm long (erect to pendent); complexly divided; bipinnate with conspicuously divided pinnules to tripinnate with conspicuously divided ultimate pinnules (the rachides and rachillae black and shining like the petiole, the ultimate pinnules lacking a midrib, fan-shaped, crenately lobed distally with broad, rounded or truncate lobes which on the fertile pinnules are recurved). The petioles shorter than the blades to about as long as the blades (wiry, black and shining); vascularised via a single strand. Leaf blades in outline more or less ovate. The venation of the lamina open (dichotomously branching to the distal lobes of the segments).
The sporangia marginal; aggregated in sori (the sori borne along the distal margins of the pinnules). The sori grouped close together towards the ends of the veins, under the recurved margins of the lobes; remaining discrete at maturity; with only a false indusium derived exclusively from the lamina margin (this in the form of a very specialized indusioid flap). The false indusia interrupted on the individual blade segments (each pseudo-indusium enclosing 2–10 sori); somewhat rectangular-elongate, not reniform. Paraphyses absent. The mature spores trilete; without a perispore.
Distribution and habitat. On base-rich substrates. Mostly near the sea, associated with basic rocks: in moist sheltered locations on limesone cliffs, grykes and rock crevices, sometimes on walls and bridges. Western Britain from Cornwall to Westmoreland, Western Ireland from W Cork to W Donegal, Man, Channel Islands, and sometimes naturalized elsewhere.
Vice-county records. Britain: West Cornwall, East Cornwall, South Devon, North Devon, South Somerset, North Somerset, South Wiltshire, Dorset, Isle of Wight, South Hampshire, North Hampshire, West Sussex, East Sussex, East Kent, West Kent, Surrey, Hertfordshire, Middlesex, Berkshire, Buckinghamshire, East Suffolk, West Suffolk, East Norfolk, Cambridgeshire, Northamptonshire, East Gloucestershire, West Gloucestershire, Monmouthshire, Herefordshire, Worcestershire, Warwickshire, Staffordshire, Glamorgan, Carmarthenshire, Pembrokeshire, Caernarvonshire, South Lincolnshire, Nottinghamshire, Cheshire, South Lancashire, West Lancashire, Durham, Westmorland, Isle of Man, Wigtownshire, Renfrewshire, Lanarkshire, East Ross, Channel Islands. Ireland: North Kerry, West Cork, Mid Cork, East Cork, Limerick, Clare, Kilkenny, South-east Galway, West Galway, North-east Galway, Dublin, Meath, West Mayo, Sligo, Leitrim, Cavan, Fermanagh, West Donegal.
Classification. Family Polypodiaceae (C.T.W.); Adiantaceae (Swale and Hassler); Adiantaceae (Stace). Order Pteridales (Swale and Hassler).
Comments. Adiantum species are readily recognised by their fan-shaped pinnules, which lack a midrib.
Illustrations. • A. capillus-veneris: Eng. Bot. 1887 (1886). • A. capillus-veneris: Sowerby and Johnson (1859). • Adiantum capillus-veneris (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’.