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Dryopteris aemula (Aiton) Kuntze, Hay-scented Buckler-fern

Account Summary

Native, locally frequent to occasional. Oceanic temperate.

1858; Smith, T.O.; Tempo.

Throughout the year.

Growth form and preferred habitats

The somewhat crimped appearance of its distinctive light-green fronds, and the long, purple stipe of the plant make this wintergreen plant a distinctive and easily recognised fern. The fronds when lightly bruised in the field give off a slight, sweet smell, but when collected and dried for the herbarium, they at first give off a much more distinct coumarin odour reminiscent of new-mown hay, and hence the English common name (Page 1997). D. aemula is a fern of permanently moist, but essentially well-drained acidic to neutral, often peaty soils of low base content. It typically occupies wooded slopes, shaded banks and sea-cliffs (Wardlaw & Leonard 2005).

Fermanagh occurrence

In upland mixed deciduous woodlands in Fermanagh, such as the Correl Glen NR, D. aemula can form the dominant ground cover over quite large areas of shaded, rocky ground on damp, acidic soils. The species is also a characteristic plant of the sheltered, N-facing, more acidic scarps of the Western Plateau. It is also found on some of the wooded islands of Lower Lough Erne, and on steep, wooded streamsides elsewhere in the county. Altogether, D. aemula has been often recorded in 80 Fermanagh tetrads, 15.2% of those in the VC. The fern is frequent in the western half of the county, particularly in moist woods and shady banks, but it is only occasional and very scattered elsewhere.

Irish occurrence

In Northern Ireland, D. aemula is noticeably more widespread in the wetter, more oceanic western parts of Cos Fermanagh, Tyrone and Londonderry (H33, H36 & H40), while in the east of the province it is largely but not entirely confined to the wooded coastal glens of Co Antrim (H39), and to more upland woods and stream-sides of south Down (H38) (Hackney et al. 1992). In the Republic of Ireland, D. aemula is quite frequent and widespread in counties along the western and southern Atlantic coasts, but is encountered much more rarely or completely absent along coastal counties in the east adjacent to the Irish Sea, and similarly rare in inland situations (New Atlas).

British occurrence

In Britain, as in Ireland, the distribution of this distinctive fern is predominantly western, extending right from the SW tip of Cornwall to Orkney (but not reaching Shetland). There are a few eastern outlying populations in damp, acid, mainly coastal ground in both Britain and Ireland, but nevertheless the predominant distribution is markedly western (Jermy et al. 1978; Wardlaw & Leonard 2005).

The slow growth rate of this species and the gradual, unhurried deployment of additional fronds after a relatively rapid spring flush of growth, means that the immature fronds of D. aemula are rather susceptible to frost both in late spring and in the autumn (ie an early winter or cold snap). The length and reliability of the frost-free period is the most likely factor restricting the distribution of the fern to markedly oceanic areas, and at the same time helps explains its absence elsewhere (Page 1997).

The inference immediately drawn from the distinctive distribution pattern of D. aemula is that it is sensitive to winter cold and late frosts, and according to Page (1997), its habitats are low-lying, "most being within about 30 m [100 ft] of sea-level, although it occasionally ascends higher, especially in Ireland". The mild influence of the Atlantic Gulf Stream has a more pronounced effect on winter, late spring and early summer temperatures in western Ireland than is the case in Britain. In eastern Ireland, D. aemula is known to ascend mountains to 370 m (1200 ft) in Co Wicklow (H20), and 440 m (1430 ft) in Co Down (H38), while in south Co Kerry in the extreme SW of the island (H1), the fern reaches an altitude of 646 m (2100 ft) on the high Reeks (Hart 1891; Brunker 1950; Hackney et al. 1992). Page (1997) therefore appears to be somewhat overstating the difference in the fern's behaviour between Britain and Ireland, since by comparison D. aemula reaches 220 m (715 ft) on the Furness Peninsula in Cumbria (VC 69), 770 m (2500 ft) in E Perthshire (VC 89), and an incredible 1015 m (3300 ft) on Braeriach in the Cairngorms (VC 96) (Wilson 1956; Halliday 1997).

European and world occurrence

This distinctive species has a pronounced western distribution in Europe as a whole, and Ireland is one of its strongholds (Page 1997; NI Vascular Plant Database 2014). It was listed as vulnerable in the Council of Europe report on the Rare, Threatened and Endemic Plants of Europe (Anon. 1977). In France, D. aemula is strictly confined to western parts of Normandy and Brittany. The remainder of its disjunct mainland continental distribution is thinly scattered along the Cantabrian coast of N Spain and Portugal. The only other known world locations for this fern are on the higher mountains of the Azores, the Canary Islands and Madeira (Jalas & Suominen 1972, Map 133; Jermy et al. 1978). In Madeira it is described as "frequent amongst rocks, in woods and along levadas throughout" (ie beside artificial open water channels) (Press et al. 1994).

The fact that Hay-scented Buckler-fern has its world distribution centred and concentrated in the British Isles, means that although it is not overall a rare or even a scarce species here in these islands, we do have a special duty to conserve and manage its sites and study its requirements on the grounds of our International Biodiversity responsibilities.

An interesting species comparision

Examination of both the British Isles and European species distribution maps indicates that there is a definite similarity between the pattern of D. aemula occurrence and that of Hymenophyllum tunbrigense (Tunbridge Filmy-fern). The match of these two physically very different species is particularly close within Britain and Ireland, but on the continental mainland H. tunbrigense has a number of additional stations in E France, SW Germany and NW Italy that are not shared with D. aemula (Jalas & Suominen 1972, Map 69; Tutin et al. 1993). D. aemula and H. tunbrigense both occur on the Sussex Weald and in a number of other disjunct sites in the cooler, more eastern areas of southern England, a fact apparently associated with local pockets of high humidity in these parts of the country (Jermy et al. 1978; Jermy & Camus 1991).

The habitat requirements of these two very different looking ferns are startlingly similar. Both require free-draining yet permanently moist soils, year-round high atmospheric humidity, plus shelter from full sun and desiccating winds. Both ferns grow in sheltered shade in a similar manner, rooted in peaty, acid soils on mossy boulders or on mossy rock slopes, forming carpets or curtains of cascading pendulous fronds. They grow rather slowly, and both can also be epiphytic on mossy tree trunks, as they are in Fermanagh, eg in the Correl Glen Nature Reserve.

Names

The genus name 'Dryopteris' was first given by the Greek physician, Pedanius Dioscorides (c. 40-90 AD), to a fern growing on oak trees, and is a compound of the Greek 'dryas' = 'oak', and 'pteris' = 'fern' (Gilbert-Carter 1964). The specific epithet 'aemula' is Latin meaning 'striving', 'rivalling' or 'imitating' (hence our familiar word, 'emulate'), and presumably this refers to D. dilatata or D. carthusiana which species D. aemula rivals in beauty and competes with in Nature (Step & Jackson 1945; Gilbert-Carter 1964; Gledhill 1985).

Threats

None.