British ferns (Filicopsida)


L. Watson and M. J. Dallwitz

Polystichum aculeatum (L.) Roth)

“Hard Shield-fern”.

P. lobatum (Huds.) Chevall., Aspidium aculeatum (L.) Sw.

Sporophyte. The rhizomes stout; ascending to erect; bearing scales.

Leaves aggregated terminally; not rooting at their tips; to tough, 20–100(–150) cm long; persistent; circinnate; complexly divided; once pinnate, with conspicuously divided pinnae, or bipinnate with conspicuously divided pinnules (the pinnae varying on different plants, from being themselves fully pinnate to lobed with only a single free pinnule, the pinnules sessile and unequal-sided, unlike those of Dryopteris spp.). Pinnae 25–50 on each side of the leaf. The petioles shorter than the blades (usually only about a fifth but up to almost half as long, clothed with more or less ovate brown scales); vascularised by several discrete strands (derived via several leaf traces). Leaf blades in outline linear, or lanceolate; leathery. The longest pinnae near the base of the blade, or about a third of the distance from the base of the blade. The venation of the lamina open.

The sporangia superficial; protected; aggregated in sori. The sori sub-orbicular (about 0.5–1 mm in diameter, in a row down each side of the midrib of the pinnule and sometimes of its basal lobe, with the vein upon which the sorus is borne continued well beyond it); remaining discrete at maturity; with a true indusium. The indusia peltate. Paraphyses absent. The mature spores monolete; with a perispore.

Distribution and habitat. In similar places to P. setiferum (q.v.), but more upland. Frequent in Britain and Ireland, common in N and W Britain, less common than P. setiferum in SW England and S Wales.

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, North Essex, Hertfordshire, Middlesex, Berkshire, Oxfordshire, Buckinghamshire, East Suffolk, West Suffolk, East Norfolk, West Norfolk, Cambridgeshire, Bedfordshire, Huntingdonshire, Northamptonshire, East Gloucestershire, West Gloucestershire, Monmouthshire, Herefordshire, Worcestershire, Warwickshire, Staffordshire, Shropshire, Glamorgan, Breconshire, Radnorshire, Carmarthenshire, Pembrokeshire, Cardiganshire, Montgomeryshire, Merionethshire, Caernarvonshire, Denbighshire, Flintshire, Anglesey, South Lincolnshire, 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, East Cork, Waterford, South Tipperary, Limerick, Clare, North Tipperary, Kilkenny, Wexford, Carlow, Leix, South-east Galway, West Galway, North-east Galway, Offaly, Kildare, Wicklow, Dublin, 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.); Dryopteridaceae (Swale and Hassler); Dryopteridaceae (Stace). Order Dryopteridales (Swale and Hassler).

P. x bicknellii (Christ) Hahne = P. setiferum x P. aculeatum and P. x illyricum (Borbás) Hahne = P. aculeatum x P. lonchitis are sterile and intermediate in form.

Illustrations. • P. lonchitis: as P. lobatum, Eng. Bot. 1860 (1886). • P. aculeatum: Sowerby and Johnson (1859). • 9 British Dryopteridaceae (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.’.