British ferns (Filicopsida)
Pteridium pinetorum C.N. Page and R.R. Mill).
Sporophyte. The rhizomes stout; creeping; hairy (tomentose, without scales).
Leaves distributed along the rhizomes; to 30–100 cm long; dying in the autumn; circinnate (the dominant pair of pinnae and the rest of the leaf unfolding simultaneously); compound; complexly divided; bipinnate with conspicuously divided pinnules (the lower pinnae broadly ovate with upwardly curving tips, 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 broadly ovate with upwardly curving tips. Pinnae 2–15 on each side of the leaf (? - often with only one main pair, each as large as the rest of the leaf, their midribs carried upturned and more or less straight). The petioles about as long as the blades (to about 7 mm diameter, when young orange red-brown with abundant reddish hairs but few if any whitish ones, becoming glabrous with maturity, containing little mucus); vascularised via a single strand. Leaf blades in outline bent towards the horizontal from the erect petiole, broadly ovate-triangular; not thin and translucent; leathery to herbaceous (glossy). The longest pinnae the lowermost. The venation of the lamina open (dichotomising to near the edge).
The sporangia marginal; 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. In open woodlands and on moors, supposedly a relic of native Pinus woodland. Central and northern Scotland, south to central Perthshire.
Vice-county records. Britain: Mid Perthshire, East Inverness-shire.
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 a 1997 treatment, Stace assumed that only two taxonomic groupings, treated as sub-species, are usefully recognisable in the N. Hemisphere. Subspecies latiusculum is confined in Britain to western Scotland.
Illustrations. • P. aquilinum subsp. latiusculum (K. Systma photo).
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’.