British ferns (Filicopsida)


L. Watson and M. J. Dallwitz

Gymnocarpium robertianum (Hoffm.) Newman

“Limestone Fern”.

Thelypteris robertiana (Hoffm.) Slosson, Polypodium robertianum Hoffm., Phegopteris robertiana (Hoffm.) A. Br., etc.

Sporophyte. The rhizomes long, slender; creeping (below ground); bearing scales, or naked (the few, small scales soon lost).

Leaves distributed along the rhizomes; to 20–55 cm long; dying in the autumn; circinnate (the vernation differing in detail from that of G. dryopteris). The unfolded leaf with each pinnule and pinna rolled separately, all enclosed in one ‘ball’. Leaves complexly divided; bipinnate with conspicuously divided pinnules to tripinnate with undivided ultimate pinnules (the second pair of pinnae often long-stalked). Pinnae 8–15 on each side of the leaf (“up to about 15”). Leaves not conspicuously bent near the junction of rachis and petiole (i.e., unlike those of G. dryopteris). The petioles longer than the blades (greenish brown, one and a half to three times its length, slender, brittle, with scales near the base and ascending to near the middle); not jointed; vascularised via a single strand. Leaf blades in outline glandular and dull green, ovate, or ovate-triangular. The longest pinnae the lowermost (but only about half as long as the rest of the blade - i.e., relatively somewhat smaller than in G. dryopteris); “rather longer than in G. dryopteris”. The venation of the lamina open.

The sporangia superficial; exposed; aggregated in sori. The sori sub-orbicular (small, borne in two rows near the margins of the segments); remaining discrete at maturity; naked and neither indusiate nor pseudo-indusiate. Paraphyses absent. The mature spores monolete; with a perispore.

Distribution and habitat. On base-rich substrates. On limestone, in open or partly shaded scree slopes and rocky places. Local in England and Wales, and rare and scattered in Scotland and western Ireland, but often naturalized on mortared walls elsewhere, especially in eastern England.

Vice-county records. Britain: South Somerset, North Somerset, North Wiltshire, Isle of Wight, North Hampshire, West Sussex, Surrey, North Essex, Middlesex, Oxfordshire, Buckinghamshire, East Suffolk, West Suffolk, West Norfolk, Bedfordshire, Northamptonshire, East Gloucestershire, West Gloucestershire, Monmouthshire, Herefordshire, Warwickshire, Staffordshire, Shropshire, Glamorgan, Breconshire, Radnorshire, Carmarthenshire, Cardiganshire, Caernarvonshire, Denbighshire, Flintshire, North Lincolnshire, Leicestershire, Nottinghamshire, Derbyshire, South Lancashire, West Lancashire, South-east Yorkshire, North-east Yorkshire, South-west Yorkshire, Mid-west Yorkshire, North-west Yorkshire, Durham, Westmorland, Cumberland, Isle of Man, Mid Perthshire, South Aberdeenshire, Mid Ebudes, East Ross, West Sutherland. Ireland: Clare, South-east Galway, East Mayo, Louth.

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

Illustrations. • G. robertianum: as Phegopteris robertiana, Eng. Bot. 1846 (1886). • G. robertianum: Sowerby and Johnson (1859). • Gymnocarpium spp. and Woodsia spp. (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.’.