Asplenium trichomanes – October 26th 2026 – Maidenhair Spleenwort and other spleenworts

Three species of Asplenium are common here in Scotland, but there are nine in Britain and over 600 in the world as a whole. The three common species occur on walls, especially old walls. Our Scottish cities were mostly constructed in the Victorian era, using locally-quarried stones stuck together with lime mortar. Such walls provide the perfect habitat for these species of Asplenium. They like the mortar.

Asplenium trichomanes by Carl Axel Magnus Lindman (1856–1928). Public domain, from Picryl.com.

Many of the spleenworts have become well-adapted to urban life, colonising the walls of buildings and surviving the hardships of traffic fumes, herbicide use, extremes of solar radiation and temperature along with general disturbance. Walls have many of the characteristics of cliffs, leading the ecologist Doug Larson and his researchers at the University of Guelph, to propose ‘the urban cliff hypothesis’, whereby the anthropogenic landscapes we call ‘cities’ provide surfaces equivalent to natural cliffs, and are thus suitable for plants and animals as substitutes for their natural habitat. Perhaps it’s too obvious to be stated as a formal hypothesis, but the idea advanced by Larson is that that modern buildings made of concrete, brick, and glass act as structural and ecological analogues of vertical cliff faces, while streets and pavements mimic horizontal rock, scree, and slopes.

Of course, it isn’t just spleenworts that colonise urban cliffs, but many lichens, bryophytes, flowering plants and animals. Urban pigeons are a good example. Even humans – our early forebears lived in caves, but today our homes include brick boxes, stately terraces, austere tenements and brutal high-rise buildings – all structures resembling the cliffs of our forebears. But let’s stick to spleenworts: to give readers an idea of how abundant our urban spleenworts are, I counted the number of records in the data from our Urban Flora of Scotland survey (2015-2025).

Brian Ballinger conducted a major survey of Scottish walls. His survey included free-standing walls, mostly in the eastern half of Scotland (Ballinger and Grace 2026). He recorded the zonation of plants on the walls, and you can see from the digram below that three aspleniums were abundant on the face of the walls. They shared the wall with over 20 other species including willow-herbs, dandelions and two alien species Buddleja davidii (Butterfly-bush) and Cymbalaria muralis (Ivy-leaved toadflax).

The red boxes show the ‘top 4’ species associated with walls in the survey reported by Ballinger and Grace (2026).

1. Maidenhair Spleenwort (Asplenium trichomanes)

According to the BSBI, the Maidenhair Spleenwort has become especially common in urban areas since 1960. This species has had a complex evolutionary journey via what is known as ‘reticulate evolution’, whereby genetic information is widely shared to form a network rather than the traditional evolutionary tree. The first people to examine this process in ferns were from the University of Leeds, in the research group of Irene Manton, a true pioneer in the cytogenetics of ferns and algae (Manton 1950). Her student John Lovis counted the chromosomes of many plants of A. trichomanes and found “The aggregate species Asplenium trichomanes includes three different cytotypes:- a diploid with n = 36 chromosomes, a tetraploid with n = 72, and a hexaploid with n = 108. Although the diploid and tetraploid cytotypes are widely though discontinuously distributed in both Northern and Southern Hemispheres, the hexaploid is known only from New Zealand. All three plants are distinguishable on morphological characters, and possess distinctive ecological preferences”.

Maidenhair Spleenwort (Asplenium trichomanes) growing on a wall. Image: Chris Jeffree.

Remarkably, Lovis found that diploid forms are strictly calcifuges (preferring acidic rocks like granite), whereas the tetraploid variations were cacicoles (thriving on alkaline, calcium-rich substrates like limestone and old mortar). Stace’s New Flora of the British Isles recognises these forms as distinct subspecies and it seems that the common wall subspecies is the calcium-loving Asplenium trichomanes subsp. quadrivalens. The subspecies are not easy to tell apart, and so many recorders do not try. There is an easy-to-use article about the differences here: https://bsbi.org/learn/resources/plant-crib/asplenium#heading5

The high frequency of this species may be partially due to its being ‘nimble’, able to exchange genetic information more readily with others and therefore adapt to new environments. However, this idea is refuted by Suter et al. (2000) who showed that the species is mostly an inbreeder.

2. Wall-rue (Asplenium ruta-muraria)

The Wall-rue, Asplenium ruta-muraria, is less complicated. To quote from the BSBI’s Atlas 2020 “A perennial, evergreen fern that occurs on limestone and other basic rocks, where it grows on steep, bare faces and in crevices; it is also found in hollowed clints in limestone pavement. In most lowland areas it is now equally, if not more abundant on mortared walls and other man-made structures”. So it is another calcium-lover. It is possible that it declined in the period where rain was more acid due to emissions of sulphur dioxide, but now that these emissions have been reduced the plant may be flourishing. I see it more often as a tiny plant, and I suspect it is frequently scraped off the wall by home-owners who see it as less attractive than A. trichomanes. I was surprised to see that it was the most often recorded in the Urbana Flora project – I would have guessed A. trichomanes to be more frequent.

Wall-rue, Asplenium ruta-muraria. Image: Chris Jeffree.

3. Hart’s Tongue Fern (Asplenium scolopendrium)

This is the familiar Hart’s Tongue Fern (previously called Phyllitis scolopendrium). Its fronds are unmistakeable, tongue-like and large. It can be seen in woodlands as well as on walls, and it seems to prefer humid, moist habitats, often seen near streams and including rocky woodlands, streamsides. It is highly shade-tolerant and can be seen in the grikes of limestone pavement.

Hart’s Tongue Fern Asplenium scolopendrium, rooted in the crack between stones of a wall. Image: Chris Jeffree.

It has changed its name frequently. Linnaeus named it Asplenium scolopendrium but others changed it, and for a long time it was called Phyllitis scolopendrium. But it can hybridise with aspleniums, so it is probably correct to restore the original name. This matter and many others are discussed in a very thorough PhD thesis by Heo (2021) which is readily available online. Heo extracted DNA from chloroplasts and found 17 types (’haplotypes’) which suggested that A. scolopendrium originated in Europe and spread westward.

4. Black Spleenwort (Asplenium adiantum-nigrum)

This is the most ‘fern-like’ of spleenworts, with pinnate leaves that taper to a triangle. It has long, stiff, glossy purplish-black or brown stems that are usually as long as the green blade itself. It is a widespread native in Europe and occurs too in America and Africa.

Along with Asplenium trichomanes it is believed to have increased in London since about 1995, due to the declining levels of air pollution by sulphur dioxide (SO₂). One study investigated how the two species of calcicole ferns—Asplenium adiantum-nigrum and Asplenium trichomanes —rapidly expanded across inner London walls starting around 1995 (Edgington, 2007).

This species forms several rare hybrids, but they are sterile with mishapen spores.

Black Spleenwort (Asplenium adiantum-nigrum), seen on Mull. Image: Chris Jeffree.

5. Rustyback Fern (Asplenium ceterach)

This is a greyish-green fern, with rust-like scales on the back of the leaves. It is a native plant in Britain, also in much of Europe and some of North Africa. It is however locally extinct in Poland, although it was historically found there and today it can be found surviving in Botanical Gardens. In Britain it is most common in the South-west. Evidently it was always so, as we read how William Turner, the 16^th Century  “Father of English botany”, wrote “..I heare say it is plentuous in the west country here in England”.

Like the aspleniums discussed above, it grows on calcium-rich substrates and especially the lime mortar of old walls, as well as natural calcareous substrates and quarries.

It is famously drought tolerant. In the image below the leaves have curled to reduce transpiration, but it can become very dry. On wetting, it recovers. Plants that can do this are called -resurrection plants’. Currently, it is a declining species in Britain, being most common in the south-west. Perhaps it will become more common as summer droughts continue to intensify.

Rustyback Fern (Asplenium ceterach), fronds curling in drought. Image: Chris Jeffree.

6. Forked Spleenwort Asplenium sepentrionale

This is a scarce plant with exacting requirements. We do not find it on walls like the other aspleniums It doesn’t look like a fern and so it is easily overlooked. It grows as grass-like but leathery leaves from cracks in acidic rocks, and sometimes on metalliferous spoil-heaps near mines. It can be found on rocks in Holyrood Park, Edinburgh. The leaves are usually slightly forked at the tip (as can be seen in the image below). It has been more common in the past, with many records from remote Scottish sites. Before 1930 it was widespread (here are just a few locations I found on the BSBI database: Dunkeld, Gruinard, Bein Dearg, Moncrieffe Hill, Gairloch). In more recent years many of these sites appear to have been lost.

Forked Spleenwort (Asplenium sepentrionale). Image: Chris Jeffree.

7. Murbeck’s Spleenwort Asplenium x murbeckii

This is a cross between Wall-rue (Asplenium ruta-muraria) and Forked Spleenwort (Asplenium septentrionale). It is known to form a back-cross with Asplenium septentrionale – the result is called Asplenium × hungaricum, but this one is even rarer than A. murbeckii. This plant is known in Britain from only two locations, one in Cumbria and the other on Arthur’s Seat (although back in 1933 it was recorded in Dunkeld).

One of the rare naturally-occuring hybrid Spleenworts, Asplenium x murbeckii. Like other spleenworts the spores are born in sori (singular = sorus). These are the clusters of spore-producing structures (sporangia) found on the underside of leaves. Image: Chris Jeffree.

8. Have aspleniums declined overall?

To answer this question fully would require a thorough (and time-consuming) search of the BSBI database. Another approach is to look at published species lists from earlier times. I came across this book online: Balfour, J. H. (1863). Flora of Edinburgh: Being a List of Plants Found in the Vicinity of Edinburgh, and here is what the author says about Asplenium locations:

For all species, it seems that most of the locations are places where there the species is no longer found. Walls are mentioned, but most of the locations appear to be rural. More work is required to trace the decline of these ferns, but we must postpone that to another day. It leaves unanswered the crucial question: is the widespread colonisation of urban walls by spleenworts a relatively common phenomenon, made possible by the cleaner air of the 21st Century?

9. Spleen?

We may wonder how the spleenwort name arose. In the ancient medical philosophy called the Doctrine of Signatures, it was believed that any plant’s physical appearance gave a “signature” or clue about which human organ it could cure. The reproductive structures on the underside of the fern’s fronds—called sori—grow in elongated, oblong lines. Ancient physicians and botanists thought these sori strongly resembled the shape of a human spleen. Hence, in 1597 the herbalist John Gerard wrote

“…the leaves boiled in wine and drunk by the space of forty days, do take way infirmities of the spleen; help the strangury, and yellow jaundice, cause the stone in the bladder to moulder and pass away, all which are performed by such things as be of thin and subtle parts: he addeth likewise that they slay the hicket, or yexing, and also hinder conception, either inwardly taken, or hanged about the party, and therefore, saith Pliny, Spleenwort is not to be given to women, because it bringeth barrenness”.

The scientific genus for spleenworts, Asplenium, is derived from the Greek words a- (meaning “not” or “without”) and splēn (meaning “spleen”), showing the ancient belief that the plant could physically unburden or cure an enlarged spleen.

References

Balfour JH (1863). Flora of Edinburgh: Being a List of Plants Found in the Vicinity of Edinburgh. Adam and Charles Black.

Ballinger B and Grace J (2026) Plants on urban walls in Scotland. British Wildlife 37, 505-512.

Farràs Martínez A et al. (2022) Exploring wild Aspleniaceae ferns as safety sources of polyphenols: the case of Asplenium trichomanes L. and Ceterach officinarum Willd. Frontiers In Nutrition, 9, 994215.

Heo N (2021). Evolutionary history and divergence of Asplenium scolopendrium complex and implications for taxonomy and conservation (Doctoral dissertation, College of Environmental Science).

Larson DW, Matthes U et al. (2000) Cliff Ecology. Cambridge.

Lovis, JD (1960). Asplenium trichomanes: a problem in the taxonomy of polyploids. Proceedings of the Linnean Society of London (171,130-130). Oxford University Press.

Lovis, JD (1958) An Evolutionary Study of the Fern Asplenium Trichomanes. PhD thesis, University of Leeds.

Manton I (1950) Problems of Cytology and Evolution in the Pteridophyta. Cambridge Univ. Press, Cambridge, England

Page CN (1997) The ferns of Britain and Ireland. Edn. 2. Cambridge University Press, Cambridge

Reichgelt T (2024). Linking the macroclimatic niche of native lithophytic ferns and their prevalence in urban environments. American Journal of Botany, 111(7), e16364.

Rumsey FJ (2022-6 ) Asplenium trichomanes L. in BSBI Online Plant Atlas 2020, eds P.A. Stroh, T. A. Humphrey, R.J. Burkmar, O.L. Pescott, D.B. Roy, & K.J. Walker. https://plantatlas2020.org/atlas/2cd4p9h.aq [Accessed 24/10/2026]

Sleep A (1980). On the reported occurrence of Asplenium cuneifolium and A. adiantum-nigrum in the British Isles. The Fern Gazette, 12(2), 103-112.

Suter M, Schneller JJ, Vogel JC. (2000) Investigations into the Genetic Variation, Population Structure, and Breeding Systems of the Fern Asplenium trichomanes subsp. quadrivalens. Int J Plant Sci, 161, 233-244. doi: 10.1086/314258. PMID: 10777447.

©John Grace