British ferns (Filicopsida)
Pteris aquilina L.
Sporophyte. The rhizomes stout; creeping; hairy (tomentose, without scales).
Leaves distributed along the rhizomes; to 30–180(–500) cm long; dying in the autumn; circinnate (the pinnae unfolding in acropetal sequence); compound; complexly divided; bipinnate with conspicuously divided pinnules (with the pinnules deeply, regularly, sometimes almost pectinately lobed, the ultimate segments broadly based and entire or sometimes the larger ones lobed at the base). The lower pinnae linear-lanceolate with drooping tips. Pinnae (2–)5–15(–20) on each side of the leaf (usually with several main pinnae on each side, their midribs carried horizontally to curving downward when young). The petioles about as long as the blades, or shorter than the blades to about as long as the blades (up to 2 m long and more than 7 mm in diameter, dark and tomentose at the base, green above and when young with abundant white hairs or brindled white and reddish hairs, becoming glabrous above when mature, containing much mucus); vascularised via a single strand. Leaf blades in outline bent towards the horizontal from the erect petiole, oblong, or ovate, or lanceolate; leathery to herbaceous (dull). The longest pinnae not the lowermost, but near the base of the blade to about a third of the distance from the base of the blade. The venation of the lamina open (dichotomising to near the edge).
The sporangia marginal; protected; aggregated in sori. The sori elongated (along the edge of the segment); remaining discrete at maturity; protected by true and false indusia combined (the true one elongate, internal to the sorus, membranous and ciliate). The false indusia continuous along the blade segments. Paraphyses absent (?). The mature spores without a perispore.
Distribution and habitat. Mainly on neutral substrates and on acid substrates. Usually on dry, light acid soils in woods, heaths and moors, often dominant over large areas. Abundant throughout the British Isles.
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.); Hypolepidaceae (Swale and Hassler); Dennstaedtiaceae (Stace). Order Dennstaedtiales (Swale and Hassler).
Comments. The rather variable P. aquilinum sensu lato occurs world-wide, and has a long history of sub-division into inadequately defined species, sub-species and varieties. In his 1997 treatment, Stace assumed that only two taxonomic groupings, treated as sub-species complexes, are usefully recognisable in the N. Hemisphere. Subspecies aquilinum represents the commonest components of the Pteridium complex in Britain (see P. aquilinum subsp. latiusculum).
Illustrations. • P. aquilinum subsp. aquilinum: as Pteris aquilina, Eng. Bot. 1887 (1886). • P. aquilinum subsp. aquilinum: Sowerby and Johnson (1859). • Pteridium aquilinum subsp. aquilinum (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’.