British ferns (Filicopsida)


L. Watson and M. J. Dallwitz

Dryopteris expansa (C. Presl) Fraser-Jenk. & Jermy

“Northern Buckler-fern”.

Dryopteris assimilis S. Walker, D. dilatata var. alpina Moore.

Sporophyte. The rhizomes short, stout; ascending to erect; bearing scales (densely scaly, with broad, soft scales).

Leaves aggregated terminally; to 30–80(–100) cm long; (sub-) persistent, or dying in the autumn (the base of the petiole decaying first); circinnate; compound; complexly divided; bipinnate with conspicuously divided pinnules to tripinnate with undivided ultimate pinnules. Pinnae 15–25 on each side of the leaf. The petioles shorter than the blades to about as long as the blades (dark brown at the base and pale or green above, with ovate-lanceolate or lanceolate entire scales which are sometimes uniformly brown but usually dark brown in the centre and pale to reddish brown at their edges, the covering usually dense at the base and less so above); about 0.4–1.2 x the length of the blade (from rather less than half as long to about the same length); vascularised by several discrete strands (derived via several leaf traces). Petiolar scales not golden brown (mid- to dark brown or darker-centred). Leaf blades in outline ovate to ovate-triangular (with all the pinnae in one plane). The longest pinnae usually the lowermost; 6–20 cm long. The pinnae not decreasing markedly in length basipetaly, the basal pinnae not or scarcely shorter than the longest pair. The lowest pinna with the lowest pinnule on the lower side much longer than the lowest one on the upper side, and often longer than the one or two adjoining it as well; with the basal pinnule on its lower side generally at least half as long as the pinna itself. The venation of the lamina open.

The sporangia superficial; protected; aggregated in sori. The sori sub-orbicular (usually relatively large, about 0.5–1.5 mm in diameter, regularly aranged in two rows along the segments); remaining discrete at maturity; with a true indusium. The indusia reniform and attached at the indentation; small and fugacious. Paraphyses absent. The mature spores pale brown; with rather small, widely spaced, acute spinules; monolete; without a perispore.

Distribution and habitat. Cool, often damp places in woods, montane crevices and scree. Locally frequent in Scotland, Wales, and England south to Westmoreland.

Vice-county records. Britain: Breconshire, Carmarthenshire, Cardiganshire, Merionethshire, Caernarvonshire, Denbighshire, North-west Yorkshire, Durham, South Northumberland, North Northumberland, Westmorland, Cumberland, Dumfriesshire, Kirkcudbrightshire, Ayrshire, Peeblesshire, Fifeshire, Stirlingshire, West Perthshire, Mid Perthshire, East Perthshire, Angus, 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.

Classification. Family Polypodiaceae (C.T.W.); Dryopteridaceae (Swale and Hassler). Order Dryopteridales (Swale and Hassler).

The apogamous D. remota (Braun ex Döll) Druce = D. affinis x D. expansa; D. x sarvelae Fraser-Jenk. & Jermy = D. carthusiana x D. expansa; D. x ambrosiae Fraser-Jenk. & Jermy = D. dilatata x D. expansa.

Illustrations. • 9 other 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.’.