Asplenium adiantum-nigrum L. s.l., Black Spleenwort
Account Summary
Native, frequent. European temperate, but also present as a disjunct rarity in C Asia and N America.
1860; Smith, Rev Prof R.W.; Florencecourt.
Throughout the year.
Growth form and preferred habitats
Black Spleenwort is a very variable evergreen perennial of well-drained, somewhat base-enriched rocky places, including limestone screes and dolomitised sandstone scarps, especially in more western, coastal and lowland parts of Britain and Ireland. The plant typically produces a loose tuft of triangular fronds from a short, creeping rhizome. It favours sheltered, lightly shaded situations where competition is reduced for a variety of reasons. In very sheltered, more deeply shaded woodlands and hedgebanks, frond length can occasionally reach 50 cm. Reduced competition often involves fern habitats with little soil such as, for instance, tree-shaded rock crevices on cliffs and on old quarry faces. Here, fronds sometimes reach up to 30 cm in length, while in more exposed sites with similar strictly limited soil resources they are always very much smaller, often only 10 cm in length or less.
Black Spleenwort also occurs, though not quite so abundantly, on limestone cliffs, and together with the modified sandstone rock mentioned, this behaviour reflects this species known soil nutrient requirement for at least a trace of base-rich elements, most likely calcium or magnesium (Jermy et al. 1978; Jermy & Camus 1991). This minimal but necessary base requirement excludes A. adiantum-nigrum from acidic siliceous rocks, such as quartzite, granite or normal sandstone (Webb & Scannell 1983), but it is not the case, as is sometimes claimed, that this species avoids limestone (Hultén 1962; Sinker et al. 1985), at least not in Fermanagh, nor in the Burren, Co Clare (H9).
Apart from hedgebanks, the fern occasionally occurs in other artificial habitats, such as on old lime-mortared walls and bridges in lowland areas.
Variation and taxonomy
In recent years, A. adiantum-nigrum has been recognised as having two subspecies: the common and widespread subsp. adiantum-nigrum, and a second one, to some extent associated with, but perhaps not totally confined to ultra-basic (especially serpentine) rock, subsp. corrunense Christ (Page 1997). The latter was previously confused with the continental European species, A. cuneifolium, and its relationship with this species remains the subject of continuing research. Serpentine and other ultrabasic (or ultramafic) rocks often supply toxic or near-toxic levels of heavy metals such as nickel, cobalt and chromium. The derived soils are extremely infertile, which greatly reduces plant vigour and competition (Brooks 1987). Within the Fermanagh western plateau, there is a crescent-shaped outcrop of intrusive dolerite and basalt which just might support subsp. corrunense, and while it has not yet been discovered, it should certainly be looked out for (Woodland et al. 1977).
Fermanagh occurrence
Black Spleenwort is a characteristic species of the dolomitised, somewhat base-enriched, sandstone scarps in the more upland SW of Co Fermanagh that is referred to as the Western Plateau. It has been recorded in 73 tetrads in the VC, representing 13.8% of the total area. The occurrence is most unevenly spread however, the fern being predominantly confined to the western half of the county. The most elevated site in Fermanagh for Black Spleenwort is at Cuilcagh Gap, around 550 m. Otherwise, the generally lowland pattern that this species displays elsewhere in the British Isles is reflected in Fermanagh (Page 1997). It also occurs, but only very occasionally, on old lime-mortared walls and bridges in the lowlands. Local examples of this occur at Tubbrid churchyard and on the old bridge at Roogagh River.
British and Irish occurrence
A. adiantum-nigrum s.l. rarely occurs in large populations, but is widely distributed throughout these isles, being most frequent in the S and W, and especially so in mild, coastal districts where high levels of humidity and illumination are the norm (Page 1997; Wardlaw & Leonard 2005).
European and world occurrence
A. adiantum-nigrum s.l. is widespread in Europe north to 63o on the W coast of Norway, and south to the Peloponnese, NW Africa, the Caucasus, N Iran, C Asian mountains, SW North America and is also found on some isolated tropical mountains and islands (Jalas & Suominen 1972; Jonsell et al. 2000). The northern hemisphere map of the species (Hultén (1962, Map 142), shows that it absent from vast tracts of temperate and boreal Asia and N America, to such an extent that to this author’s mind it does not warrant inclusion in an atlas of circumpolar plants. The later publication of A. adiantum-nigrum s.l. world distribution (Hultén & Fries 1986, Map 44), again highlights how very far removed the species is from being circumpolar. Preston and Hill (1997) classified the fern as European temperate, at the same time noting that it has an additional very restricted presence in N America, occurs in C Asia and also in widely disjunct parts of the tropics and the Southern Hemisphere, including Australia and Hawaii (Hultén & Fries 1986).
Names
'Asplenium' is derived from the Greek 'a' meaning 'not' and 'splen', 'splene' or 'splenon' referring to the spleen, alluding to the supposed medicinal properties of the fern genus. The herbal medicinal use is also invoked by the English common name applied to the genus, ‘Spleenwort’ (Hyam & Pankhurst 1995). The specific epithet is ‘adiantum-nigrum’. ‘Adiantum’ is Greek, ‘a’ meaning ‘not’ and ‘diantos’, moistened, and thus the combination ‘adiantos’ means ‘dry’, ‘not wetting’ or ‘unwetted’, referring to the fact that fronds of the fern genus ‘Adiantum’ remain unwetted under water. ‘Nigrum’ means ‘black’, so ‘adiantum-nigrum’ translates literally as ‘dry black’ or ‘unwetted black’. However, as the fern Adiantum capillus-veneris has the English common name ‘Maidenhair Fern’, Asplenium adiantum-nigrum in the past was given the book name ‘Black Maidenhair Spleenwort’. Since there already is a fern with the given (book) name ‘Maidenhair Spleenwort’ (Asplenium trichomanes), to avoid confusion A. adiantum-nigrum is most usually referred to as ‘Black Spleenwort’ (Step & Jackson 1945).
Although A. adiantum-nigrum is very widely distributed in both Britain and Ireland, it does not appear ever to have had a genuine folk-name or English common name, only the invented, given, book names listed above. Lyte (1578), in his ‘Niewe Herball’ mentions this fern under the names ‘Black Oak-fern’ and ‘Petty-fern’, but in reporting this information Step and Jackson (1945, p. 51), express their doubt that these names would have been in use among the people at that early date.
Herbal medicinal uses
Black Spleenwort is said by herbalists to have similar medicinal virtues to other Maidenhairs, “a decoction of it relieving a troublesome cough and proving also a good hair wash. Dosage of infusion: 3 tablespoonfuls” (Grieve 1931, p. 303). Allen and Hatfield (2004) reported that in Ireland a cough cure known as ‘maidenhair’ was once popular among country people in Londonderry (David Moore unpublished report 1834-5). These latter authors assumed that this referred to Maidenhair Spleenwort (A. trichomanes), but it might equally well have been A. adiantum-nigrum that was used. Adiantum capillus-veneris does not come into the question on this matter since it was always a rare plant of very restricted distribution.
Threats
None.