Dryopteris carthusiana (Vill.) H.P. Fuchs, Narrow Buckler-fern

Account Summary

Growth form, identification and preferred habitats

This deciduous, bipinnate fern is very much a species of wet, peaty, cut-over lowland raised bogs and lakeshore marshes and fens, especially those overlying rich alluvial soils. The lightish-green upright fronds with long basal stipes are usually produced in sparse, irregular groups (never in tight shuttlecocks), which makes it easy to distinguish the species even at some distance from the much more robust and very much more common D. dilatata (Broad Buckler-fern).

The plant has either a short, decumbent rhizome crown (ie reclining but rising at the tip), or a more slender creeping rhizome, the latter type spreading through wet peat and mossy cushions and branching to produce new crowns which send up groups of aerial fronds at intervals.

In our Fermanagh experience, there often may be only one or two individual fronds sprouting in 30 cm high vegetation on a large expanse of bog, so that this is a species that must be actively searched out. Once one has developed an eye for its particular habitat and manner of growth, however, it can be found quite frequently.

The literature suggests that D. carthusiana occurs as a plant of wet woodlands, usually with an alder-willow-birch canopy and with a floor dominated by Sphagnum bog mosses (Page 1982, 1997). However, we do not find it under these conditions anywhere in Fermanagh.

Fermanagh occurrence

In Fermanagh, D. carthusiana has been recorded in 62 tetrads, 11.7% of those in the VC. Seven of these tetrads have pre-1976 records only, a proportion that suggests that the habitats this fern occupies are under threat (see below). As the distribution map indicates, Narrow Buckler-fern is very widely but rather thinly scattered, mainly across wetter areas of the Fermanagh lowlands.

Reproduction

In addition to vegetative spread, mature fronds produce numerous asexual sori, which spore freely from July to September (Hyde et al. 1969). The fronds are summer-green only, dying and disappearing quickly after the first winter frost (Jermy & Camus 1991; Page 1997). Interestingly, in Scandinavia, Jonsell et al. (2000) suggest that it is the fertile fronds which die off, while most sterile ones persist overwinter.

British and Irish occurrence

D. carthusiana is widespread in lowland area of both Britain and N Ireland, especially in Britain south of a line between Stranraer and Berwick-upon-Tweed, and in Ireland, north of the International border with the Republic. However, its frequency has quite rapidly declined throughout these islands since the 1930s. The decline is perhaps most obvious in Ireland where the species was never all that frequently reported to begin with, although there remains an outside and unlikely possibility that the species may not be discriminated by sufficient Irish field workers to give an accurate picture (Jermy et al. 1978; Webb et al. 1996; Page 1997). Irrespective of this possibility, there can be no doubt that Narrow Buckler-fern was much more familiar and frequently found by Victorian field botanists than it is today, since it is now a locally frequent to occasional, or even a rare species in parts of the British Isles (Webb et al. 1996; Page 1997).

Being a plant of wet, peaty habitats which naturally follow a transitional pattern of dynamic succession gradually moving towards drier seral stages as organic matter accumulates, it is not surprising that D. carthusiana populations are eventually eclipsed by these environmental and vegetational changes. They are also vulnerable to the much more drastic and rapidly operating effects of artificial drainage for farming, peat-cutting or other land-development processes which have increasingly affected lowland wetlands in Britain and Ireland during the last 50 or more years (Jermy & Camus 1991).

European and world occurrence

In continental Europe and W Asia, D. carthusiana is widespread in mid-temperate latitudes of N and C Europe thinning somewhat northwards (although reaching within the Arctic Circle in Scandinavia), and southwards to the Mediterranean (Jalas & Suominen 1972, Map 129). Related forms or species occur in eastern N America allowing Hultén (1958, Map 155) to include D. carthusiana (as D. spinulosa) in his amphi-Atlantic group of species. In eastern and central N. America there are closely related taxa that Hultén and Fries (1986, Map 67), plot as var. intermedia and var. fructosa.

In Scandinavia, D. carthusiana appears to occupy a much greater range of habitats than in Britain and Ireland, including much drier sites such as rock crevices, screes, tall-herb meadows and dunes, as well as on stone walls and urban situations (Jonsell et al. 2000).

Name

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 Latin specific epithet 'carthusiana' refers for some unknown reason to the Grande Chartreuse Monastery of Carthusian Monks, near Grenoble, in France (Gledhill 1985).

Threats

Drainage of fens and bogs, and mechanical peat cutting.

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