British ferns (Filicopsida)


L. Watson and M. J. Dallwitz

Cystopteris fragilis (L.) Bernh.

“Brittle Bladder-fern”.

Sporophyte. The rhizomes short, rather stout; more or less decumbent; bearing scales (these thin, brown, lanceolate). Plants with no clear distinction into fertile and sterile leaves.

Leaves aggregated terminally; to (5–)10–35(–45) cm long; dying in the autumn; circinnate; compound; complexly divided; bipinnate with conspicuously divided pinnules to tripinnate with undivided ultimate pinnules (the pinnules deeply pinnatifid, ultimate segments sharply toothed, serrated, or bluntly lobed). Pinnae 5–15 on each side of the leaf (? - “up to 15”). The petioles shorter than the blades to about as long as the blades (from a third as long, slender and brittle, dark brown at the base and paler above, with a few scales at the base and usually a few hair-like scales above). Leaf blades in outline lanceolate. The longest pinnae about a third of the distance from the base of the blade to around the middle of the blade; 1–4 cm long. The adjacent pinnae approximated but not strongly overlapping to distant from one another and not at all overlapping (the separation becoming less marked acropetaly). The venation of the lamina open. The veins of the ultimate pinnules terminating in the apices of their teeth.

The sporangia superficial; protected; aggregated in sori. The sori sub-orbicular (small, each on a receptacle with a vascular strand from the vein, borne in two rows, one on either side of the midrib of the pinnule); remaining discrete at maturity; with a true indusium. The indusia not reniform but flap-like from the base of the sorus, vaulted at first, later reflexed; whitish, ovate, acuminate or toothed, exceeding the sorus. The mature spores echinate; without a perispore.

Distribution and habitat. On base-rich substrates. In basic soils, on shady rocks, walls and in rocky woods, also on mortar in walls in acid areas. Common in northern and western Britain, scattered in S and E, and frequent but scattered in Ireland.

Vice-county records. Britain: West Cornwall, East Cornwall, South Devon, North Devon, South Somerset, North Somerset, North Wiltshire, South Wiltshire, Dorset, Isle of Wight, South Hampshire, North Hampshire, West Sussex, East Sussex, East Kent, West Kent, Surrey, South Essex, Hertfordshire, Middlesex, Berkshire, Oxfordshire, Buckinghamshire, East Suffolk, West Suffolk, East Norfolk, Cambridgeshire, Bedfordshire, Northamptonshire, East Gloucestershire, West Gloucestershire, Monmouthshire, Herefordshire, Worcestershire, Warwickshire, Staffordshire, Shropshire, Glamorgan, Breconshire, Radnorshire, Carmarthenshire, Pembrokeshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Denbighshire, Flintshire, Anglesey, North Lincolnshire, Leicestershire, Nottinghamshire, Derbyshire, Cheshire, South Lancashire, West Lancashire, South-east Yorkshire, North-east Yorkshire, South-west Yorkshire, Mid-west Yorkshire, North-west Yorkshire, Durham, South Northumberland, North Northumberland, Westmorland, Cumberland, Isle of Man, Dumfriesshire, Kirkcudbrightshire, Wigtownshire, Ayrshire, Renfrewshire, Lanarkshire, Peeblesshire, Selkirkshire, Roxburghshire, Berwickshire, East Lothian, Midlothian, West Lothian, Fifeshire, Stirlingshire, West Perthshire, Mid Perthshire, East Perthshire, Angus, Kincardineshire, 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, Orkney islands, Shetland, Channel Islands. Ireland: South Kerry, North Kerry, West Cork, Mid Cork, Waterford, South Tipperary, Limerick, Clare, North Tipperary, Kilkenny, Wexford, Carlow, Leix, South-east Galway, West Galway, North-east Galway, Offaly, Kildare, Wicklow, Meath, West Meath, Longford, Roscommon, East Mayo, West Mayo, Sligo, Leitrim, Cavan, Louth, Monaghan, Fermanagh, East Donegal, West Donegal, Tyrone, Armagh, Down, Antrim, Londonderry.

Classification. Family Polypodiaceae (C.T.W.); Cystopteridaceae (Swale and Hassler); Woodsiaceae (Stace). Order Athyriales (Swale and Hassler).

Illustrations. • C. fragilis: as Dryopteris fragilis, Eng. Bot. 1864 (1886). • C. fragilis: Sowerby and Johnson (1859). • C. fragilis var. dentata: Eng. Bot. 1865 (1886). • C. fragilis var. dentata: Sowerby and Johnson (1859). • C. fragilis var. angustata: Sowerby and Johnson (1859). • Cystopteris species (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.’.