Woodsia ilvensis
Status Schedule 8, Wildlife & Countryside Act (1981). UK Biodiversity Action Plan Priority species. Red Data Book. IUCN Threat category: Endangered (2005). Taxonomy Pteropsida: Athyriaceae Scientific name: Woodsia ilvensis (L.) R. Br. Common names: Oblong Woodsia, Coredynen Hirgul
Woodsia is one of six genera in Britain belonging to the fern family Athyriaceae. It is characterised by having the indusium divided into a fringe of hair-like scales around the base of the sorus (Figure 4).
There are 25 Woodsia species world-wide in the temperate and cool temperate zones, of which two occur in Britain, W. ilvensis (Fig. 1) and W. alpina (Fig. 2). Both are found in the mountainous regions of the British Isles grow in similar places but W. alpina is most characteristic of base-rich rock types.
Biology & Distribution Figure 1. Woodsia ilvensis Very local in Caernarfonshire, Cumberland, Dumfriesshire and Angus, decreasing and formerly more widespread (Preston et al. 2002). Current populations are probably relicts of a more widespread post-glacial distribution. It suffered serious declines due to collecting in the 19th century. There have been re-introductions in Scotland and Teesdale which were not mapped by Preston et al. (2002).
It grows in cracks and fissures in cliffs and crags on rocks ranging from calcareous tuffs and hornblende schists to more acidic tuffs, grits and shales. Sites are very free-draining, with little competition. Reproduction is mostly vegetative.
Identification & Field survey The two Woodsia species can be readily separated using the characters given in the table overleaf. In addition, small forms of Cystopteris fragilis (Fig. 3) have been mistaken for Woodsia, but differ in having glabrous fronds and a membranous indusium Figure 2. Woodsia alpina (Fig. 4b). Differentiation from similar species
Woodsia ilvensis (Fig. 1) Woodsia alpina (Fig. 2) Frond length to 10(-15) cm to 8(-15) cm including stalk (stipe) Stalk length half as long to as long as the midrib quarter to two-thirds as long as the midrib of of the blade the blade Hairs with flexuose hairs throughout rather sparsely hairy with flexous hairs Scales c. 2-3 mm long, on underside of c. 1-2 mm long, only on stalk, midrib and blade midribs of the pinnae Pinnae 7-15 on each side 5-10 on each side Longest pinnae oblong to ovate-oblong and c. 1.5-2 triangular-ovate and c. 1-1.5 times as long as times as long as wide, with 3-8 lobes wide, with 1-4 lobes on each side on each side Spores [use 42-50 microns diameter 50-57 microns diameter microscope with graticule]
References Brown, D. F. M. (1964). A monographic study of the fern genus Woodsia. Beih. Nova Hedwigia 16: 1-154 Condry, W. M. (1987). Dwy redynen brin o Eryri. Y Naturiaethwr 17: 2-5. Hutchinson, G. & Thomas, B. A. (1996). Welsh Ferns. 7th edn. National Museums and Galleries of Wales, Cardiff. Mitchell, J. (1995). Setting up a monitoring system for Woodsia in the west of Scotland. Pteridologist 2: 285-287. Page, C. N. (1997). The Ferns of Britain and Ireland. 2nd edn. Cambridge University Press, Cambridge. Preston, C.D., Pearman, D. A. & Dines, T. D., eds. (2002). New Atlas of the British & Irish flora. Oxford University Press, Oxford. Rickard, M. H. (1972). The distribution of Woodsia ilvensis and W. alpina in Britain. British Fern Gazette 10: 269-280. Wigginton, M. J., ed. (1999). British Red Data Books. 1. Figure 3. Cystopteris fragilis. Vascular plants. 3rd edn. Joint Nature Conservation Committee, Peterborough.
Additional photographs are available on the ARKive website (http://www.arkive.org/species).
a b
Figure 4. a Woodsia indusium; b Cystopteris indusium.