Asplenium ruta-muraria L., Wall-rue

Account Summary

Growth form and preferred habitats

This small tufted evergreen perennial is locally abundant on natural habitats such as narrow crevices in rocks and cliff faces, almost exclusively growing on limestones or other forms of base-rich rock. Otherwise this lime-tolerant, strongly calcicolous species is almost exclusively a plant of the lime-rich mortar of old walls and bridges, and it is particularly abundant on rural examples of these man-made habitats. It develops most luxuriantly in half-shaded, damp sites.

Page (1997) rather tentatively suggests that A. ruta-muraria is, "a fast-growing and perhaps rather short-lived spleenwort. In most situations, frequent re-establishment occurs ...". There appears to be very little evidence of dead plants and turnover taking place on walls in Fermanagh, and the reproductive behaviour of Wall-rue requires and deserves further study.

Fermanagh occurrence

Widespread in Fermanagh, this small, tufted, evergreen fern has been recorded in 153 tetrads, 29.0% of those in the VC. Nine of the tetrads have pre-1976 records only. It is very common throughout the county, mainly on calcareous rocks, including in shaded crevices in the limestone pavement above Florencecourt and around Knockmore. However, it also grows on the dolomitized sandstone scarps in the more upland, rather exposed and somewhat wetter Western Plateau. Some stretches of the red sandstone scarps here have been chemically altered by long-term percolation of calcium- and magnesium-rich water derived from overlying rocks (ie., they have become dolmatized).

British and Irish occurrence

Wall-rue is very common throughout Britain and Ireland. However, being calcicole and sensitive to atmospheric pollution, A. ruta-muraria is much less frequent or scarce in more urban and industrial areas of Britain and Ireland, and in regions where soils are predominantly acidic. This includes substrates derived from siliceous igneous and metamorphic rocks that make up the structure of N Scotland and N & W Ireland. Rarity also applies in oceanic areas of very high rainfall, where strongly acidic peaty soils develop, irrespective of the geochemistry of the underlying rock (Jermy et al. 1978; Jermy & Camus 1991; New Atlas).

European and world occurrence

This fern is widespread across W & C Europe and extends north of the Arctic Circle (Jalas & Suominen 1972). The species has its headquarters in more central areas of Europe, and geographically is considered a continental species, albeit with a particularly extensive range near to the western Atlantic coast (Page 1988, p. 86).

The circumpolar distribution of A. ruta-muraria is decidedly disjunct, the species being entirely absent from W and C regions of N America, and poorly represented with very few, widely spaced sites in E Asia (Hultén 1962, Map 156).

Hultén (1962) described the species as being, "fairly variable, at least 15 varieties having been described from C and S Europe, Morocco and China". Two subspecies of differing chromosome count are recognised in Europe, but only the tetraploid, subsp. ruta-muraria, is recorded in Britain and Ireland (Page 1997). A counterpart, confined to eastern N America, has been described as a distinct species, A. cryptolepis, but Hultén (1962) preferred to consider this plant a further subspecies of A. ruta-muraria.

Extremely rare hybrids

Although Wall-rue commonly occurs immediately adjacent to A. trichomanes subsp. quadrivalens (Maidenhair Spleenwort) in both natural habitats and on walls, the hybrid between them, A. × clermontiae (Lady Clermont's Spleenwort), has only once occurred in the British Isles – in 1863 on a mortared wall in Co Louth, Republic of Ireland (H31). It has not been found in Co Down (H38) as erroneously reported by Stace (1975) and repeated by Page (1997) (Hackney et al. 1992).

A. ruta-muraria does also form another very rare hybrid with A. septentrionale (A. × murbeckii), which has never been recorded anywhere in Ireland, but has been found three times in Britain, and has also been reported in 13 Scandinavian provinces (Stace 1997; Jonsell et al. 2000).

Names and Uses

'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 Latin specific epithet 'ruta-muraria' translates as 'Rue of the wall' or 'Wall-rue'. Folklore suggested that wearing A. ruta-muraria could protect the individual from witchcraft. The unrelated flowering plant, Rue (Ruta graveolens) with bluish-green leaves, was a symbol of sorrow and repentance, and as such could be used either to bless or curse, help or harm. In the absence of flowering Rue, the fern, Wall-rue, could be used as a substitute (Vickery 1995).

Wall-rue had the alternative and rather mysterious English common name, 'Tentwort' (Page 1988). The original version of this name was 'Taintwort', from its use as a remedy for 'the taint', better known to us as rickets (Step & Jackson 1945). Other names applied to the fern include 'White Maidenhair', from the fronds sometimes taking on a blue-green appearance (Gerard 1597), and 'Stone Rue' (Lyte 1578). Herbalists considered it a good remedy for coughs and ruptures in children. It was also thought to prevent hair falling out, and was used for treating shortness of breath, yellow jaundice, diseases of the spleen, stopping of the urine, and to help break up kidney stones. Grieve (1931, page 303) details these and many other herbal medicinal uses of this fern.

Threats

None.

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