I've been a fern freak for as long as I can remember, but I read Botany at University and this, especially the field trips to Wales, educated my interest, particularly in the spleenworts. Because these are mostly small and grow unobtrusively on old walls, most people dismiss them as opportunist weeds. But seen close up they are, in my opinion, amazingly beautiful as I shall try to demonstrate on this page. Wall rue (Asplenium ruta-muraria), the smallest native fern in the UK, always fascinated me because of its ability to thrive in the harsh environment of old mortar. I wondered how old a wall had to be to support wall rue. Now I know - I'll give you the answer shortly.
We moved to our present house in Rugby in 1981. This part of the town was developed around 1900. Our garden wall dates from that time. There were no ferns on it when we moved in. Over the years first hartstongues (Asplenium scolopendrium) and then black spleenworts (Asplenium adiantum-nigrum) appeared on it, followed by male ferns (Dryopteris filix-mas), which are now becoming dominant; they're big enough to overshadow the other species. About five years ago (2007) wall rue appeared on a wall in an alleyway about 50 metres away and that colony is now thriving. In February 2011 I spotted the first wall rue on our wall, peeping out from beneath the fronds of a much larger hartstongue. Since then I've photographed it at regular intervals and watched it develop into a mature stand. There are three other stands of it on the wall, but these are developing more slowly, still consisting mostly of embryonic fronds. So, to answer the question raised in the previous paragraph, in this part of Rugby a wall needs to be about 100 years old to support wall rue, but I imagine that the figure will vary widely depending on the type of mortar, moisture availability, light and numerous other factors. Incidentally, our garden wall is south-facing, but the fern-populated part of it is shaded by the house for most of the day.
I've propagated wall rue from spores. Specimens grown in artificial conditions look a little different from those that eke out a living on walls. They are generally more luxuriant as the following illustration shows.
Observing the ferns on the wall has been fascinating. In the mortar there are dozens of young ferns, most of which get eaten by snails (there's a huge population of those) before they become mature. One whose shape appealed to me is depicted below, photographed on 15 July 2012. This one sadly got eaten by a snail before I could identify it.
Later on I discovered what species this was. In July 2013 our neighbours who own the wall announced that they intended to demolish it because it's not safe. It's provided me with over four years of interesting observations of fern colonisation, but I'd hate it if the wall fell on anyone, so I bow before the inevitable. I decided to rescue a few of the black spleenworts before demolition as these are only 'locally abundant' and in the course of doing this discovered that what I had dismissed as yet another juvenile male fern certainly was not. It proved to be Polystichum aculeatum, hard shield fern. Apologies, until recently I thought it was the closely related soft shield fern, P. setiferum, which is cultivated in some gardens locally. I have never come across P. aculeatum locally, however, and I have never heard of either species growing in mortar. (One of the joys of being a fern freak is that you never know what you will come across - ferns have very broadly based territories.) I rescued this one and potted it up. When I purchased C. N. Page's excellent The Ferns of Britain and Ireland under the entry for Polystichum setiferum there was a picture of an immature frond rather like that in the pic above. So that too had been a Polystichum. Later I replanted the rescued fern beneath a Buddleia in the garden to simulate a woodland environment. Although P. aculeatum is not a woodland species, it's doing fine as the following picture taken on 25 April 2015 shows. There are at least six new fronds in the process of unwinding. And this makes a total of five fern species on the wall.
Maidenhair (or common) spleenwort (Asplenium trichomanes subs quadrivalens) is another favourite of mine. I love its its neatly paired pinnae and the fact that it's cosmopolitan, occurring in all continents. We joke that the Mars explorer vehicle will find it well established on the red planet, growing on the wall of the Martian Irish pub (well, they occur everywhere as well, don't they?) It hasn't appeared on our garden wall yet, but there's plenty in the neighbourhood so it may yet do so. In fact I decided to cheat Nature and introduce it artificially into my rockery. Attempts at transplanting mature samples from nearby failed and so I'm propagating new plants from spores with a view to establishing the young ferns in the rockery in the future.
It's been fascinating watching the ferns develop. Not only is every frond different - more complex than the previous - but also every plant is different, as though the Creator gave this species free rein to develop as it wishes.
I sowed the spores on sterilised soil in a transparent plastic container. Inevitably some spores stuck to the sides, but nevertheless developed into prothalli (the 'other' stage in the life cycle of a fern) clinging right there on the vertical plastic. What is remarkable is that these produced new fern plants right there on the shiny vertical plastic surface faster than those growing on supposedly 'good' soil! Well, let's face it, this species is an expert at living on walls. When I transferred one of the wall-growing plantlets to a flowerpot, it appeared that its root had penetrated the plastic. Incidentally, as with wall rue, maidenhair spleenwort grown in artificial conditions looks a little different to examples growing on walls; the pinnae are larger, rounder and more widely spaced than on young specimens seen on walls.
Hartstongue (Asplenium scolopendrium although it was Phyllitis scolopendrium when I was at University) is the only UK-native fern species that has undivided fronds. Another interesting fact about it is that, although it is widely distributed in the Northern hemisphere, it is only in Britain that it is very common; elsewhere it is one of those species that you come across occasionally. Soon after we moved into our house I planted one in the garden. Thirty years later it is still thriving - so much so that according to the reference books it is somewhat over the maximum size for the species. A good thing it can't read.
It's well known that hartstongues vary somewhat in the form of their fronds. The one pictured below was an interloper when I propagated wall rue from spores. Two prothalli were clearly about ten times the size of the others and one of these developed a sporophyte that at first I couldn't identify so I left it to grow. This is what it became: forked hartstongue. Unfortunately, since the below pic was taken the forked fronds have been replaced with conventional ones.
When we moved into our house in 1981 I discovered quite a population of hartstongues and male ferns in the light well to our cellar. This is covered by a cast-iron and glass 'lid' which is waterproof - certainly no rain gets in. But recently I was amused to spot the sight shown below: although the rain can't get in, the hartstongues can get out! Quick, nurse, they're escaping!
There's a lot of advice on this in books, but I'd like to give two snippets of my own that may be contrary to what you've read elsewhere:
At the start of 2012 I joined the British Pteridological Society and have found their website and publications very useful. I heartily recommend this organisation to anyone interested in ferns or wanting to learn more about them.
OK, so it's not a fern ... at least, not quite. It's a liverwort. But it doesn't take a lot of imagination - those pale green sporangiophores probably photosynthesise; all they need is a vascular system and a proper root and they could, like fern plants, live independently of the gametophyte which is anologous to the fern prothallus that it resembles. Those conspicuous gemma cups allow the liverwort to spread asexually when raindrop splashes disperse the gemmae (buds) that they contain - and I've seen fern prothalli reproduce asexually by budding as well (although the text books never mention this). It's not hard to see the course that evolution took.
As one who became a Christian while a biological sciences student I have never had any difficulty in reconciling evolution with a Bible-based faith. To me it seems perfectly reasonable that a loving Creator, concerned about his living creation, would build into it a means by which it can adapt to long-term changes in the environment. And even to use this process as a tool of creation. After all, both science and the Bible teach us that creation is still in progress - the cosmos is not yet complete.
© Roger Amos 2015