Wild Wall

It’s a wall like hundreds of other such walls in the city, an old remnant of some enclosure long forgotten. It’s been heightened in a more recent period, although it’s not clear why.  ‘Round back’ of a plumbing supply place in Cork, people walk and drive by it every day without a second glance. But if you pause and take a close look it rewards with an astonishing variety of plant life.

In their magnificent book The Wild Flowers of Ireland:The Habitat Guide Declan Doogue and Carsten Krieger devote a chapter to Old Walls and Ruins. Here’s how they introduce that chapter: Walls, they say

. . .have over time been colonised by a number of plant species, some of which seldom live elsewhere in Ireland. . . . Buildings are completely artificial structures. Therefore the question arises as to where these colonising species lived before these walls were built. Some species were either deliberately or accidentally introduced by man into the country, usually for medicinal or ornamental reasons, within the past 1000 years and have become established or persist on walls. Another group of genuinely native Irish species made their own way, spreading from natural and usually rocky habitats within the Irish countryside onto the new buildings of the time. In both cases there were enough points of environmental similarity between the plants’ original natural habitats and the buildings of the Irish countryside to make it possible for them to extend their range and find new homes. In a sense an ongoing botanical battle between the native and newcomer was being fought on the fabric of these old buildings. This struggle comes complete with issues such as natural succession, colonisation, displacement, local extermination and sheer opportunism. The conflict continues to this day and can be observed in most older towns and cities.

Walls have other characteristics friendly to certain plants: the stones warm up in the sun and retain their heat into the evening, acting, as Doogue and Krieger put it, as a sort of storage heater. Lime-rich mortar allows lime-adapted plants to flourish even in non-lime areas. Microclimate and soil conditions on top of the wall can be different from those on the sides, or on south-facing versus north-facing walls.

This wall in Cork exemplifies everything Doogue and Krieger describe – native and non-native species growing side by side in an environment where it seems impossible that enough nourishment could be supplied.

Oxford Ragwort

Some of the plants have intriguing histories. Take the humble Oxford Ragwort, the one that looks like a yellow daisy. (This is not to be confused with Common Ragwort, or Buachaláns as they’re known in Ireland, which are on the Noxious Weeds list – although that’s another story.) It was introduced into an Oxford botanic garden in 1690 from Sicily, but soon escaped and was seen all over the walls of Oxford. The University of Bristol takes up the story from there:

During the Industrial Revolution, Oxford became a thriving railway centre and Oxford ragwort found a new habitat in the clinker beds of the railway lines that fanned out of Oxford to all parts of the country. These ‘furnished the plant with a replica of the lava-soils of its native home in Sicily’, said Druce in his Flora of Oxfordshire. Referring to the fruits (achenes) of Oxford ragwort, he said ‘I have seen them enter a railway-carriage window near Oxford and remain suspended in the air in the compartment until they found an exit at Tilehurst’ (near Reading).

Because this species hybridises readily with other Senecio species (other Ragworts and Groundsel), this site adds, the introduction and spread of the promiscuous Sicilian S. squalidus has resulted in a great deal of evolutionary novelty among British Senecio – an amazing example of evolution in action. I love the idea of a promiscuous plant.

Herb-Robert – surely one of our most-loved wildflowers

Herb-Robert is among our most commonly seen (and known) native wildflowers – a dependable spot of brilliant colour almost all year round in a huge variety of environments, with its frondy leaves turning a brilliant red as the season wears on. However, on this wall it was joined by a cousin – Shining-Crane’s-bill.

And this is Shining Crane’s-bill!

In fact, I had to do a double-take, as I had never seen this flower before and at first I thought I was looking at a miniature Herb-Robert. While it might be easy to confuse the flowers, the leaves are totally different, with the Shining Crane’s-bill leaves being smooth and hairless, almost waxy, with a distinctive shape. I wish all similar species were this easy to tell apart upon close inspection!

Shining Crane’s-bill – the flowers are smaller than Herb-Robert and the leaves are totally different

One of my favourite wall species has to be Ivy-leaved Toadflax – not a very pretty name for a truly spectacular flower. This is another Mediterranean plant, and we can blame Oxford for this one too, as it is thought to have hitched a ride on marble sculptures imported from Italy to Oxford in the seventeenth century. Once the flowers are finished, the seed heads bend away from the sun and towards the wall, dropping their seeds into the cracks – thus they are able to grow vertically up the wall.

Ivy-leaved Toadflax – every well-dressed wall should have some

At the bottom of the wall I thought I saw the ubiquitous dandelion, but once I looked closer I saw that the leaves were quite different. I think this is Smooth Sowthistle. Zoe Devlin of Wildflowers of Ireland tells me that the leaves can go this purplish colour in the absence of good soil. There are so many wildflowers that look, more or less, like dandelions – it has been a real journey of discovery to find out more about this large flower family.

Smooth Sowthistle and Ivy-leaved Toadflax in the act of climbing up the wall

Smooth Sowthistle is edible when young and has been used as fodder for animals. According to one authority I read, In Greek mythology Theseus is said to have eaten smooth sow-thistle to gain power before leaving to slay the Minotaur in its Cretan labyrinth, where it dined on human bodies, bull’s heads and young Atheneans.

Rue-leaved Saxifrage. It’s also pictured in the lead photograph at the head of the post, where you can see the basal rosette

Growing from the mossy ridges in the wall was a delicate little white flower with a reddish basal rosette, and this turned out to be Rue-leaved Saxifrage. Although it was new to me, this little native beauty is common in many parts of Ireland. As the season progresses the stem, leaves and rosette become redder – hence ‘rue-leaved.’

Red Valerian sprouting from the wall, with Oxford Ragwort and Ivy-leaved Toadflax. The tiny fern growing in the cracks glories in the name Maidenhair Spleenwort

We all know the plant known as Red Valerian, yet another Mediterranean import. I saw it growing in huge masses in the Burren a couple of years ago, meaning it’s one of those plants that enjoys the lime-rich environment provided by the mortar in the wall.

This is not, by the way, the Valerian that the sleep-aid tea is made from, the one that makes cats go loopy. It can also come in shades of pink and white, all growing side-by-side.

Keel-fruited Cornsalad (above) is also known as Lamb’s Lettuce, although it doesn’t look like the supermarket variety known by the same name. It is, in fact, very edible, with a kind of parsley after-taste and packed with vitamins (although you probably shouldn’t pick it anywhere near dog-height). The tiny blue/purple flowers reward examination through a hand-lens if you have one.

It took me a while to identify one little plant growing close to the pavement (above). It turned out to be Petty Spurge and, although it is not native to Ireland it’s been here a long time and has spread widely. It’s not usually as red-tinged as this when you see it in ID sources. It’s of huge interest to scientists at the moment because of the potential of its sap (a toxic latex substance) to treat common forms of skin cancer. Several rigorous double-blind studies have come to the same conclusion that it is an effective treatment for non-melanoma lesions. It’s a hardy little thing too – seeds found in excavations, dormant for a hundred years, can still germinate.

Finally, up on top of the wall is sprouting a Butterfly-bush (above); many of us know it as Buddleia. It’s well named, as butterflies love it. It was introduced into Europe by missionaries returning from China and it spread quickly as it will grow just about anywhere. What you see on this specimen are the remains of last year’s flowers: by June it will be hosting butterflies. Butterfly Bush may seem benign but like many other introduced species there is a dark side. First of all, as Tony O’Mahony points out in his Wildflowers of Cork City and County, it’s quite invasive and can take over and crowd out native species. The roots can do significant structural damage to the very walls it depends on for survival. More serious is the charge that, while it provides nectar for butterflies it is not a butterfly host plant – that is, one that butterflies can use to deposit their larva, which will then feed on the leaves. According to a spokesperson concerned about the destruction of chalk grasslands at Folkestone Warren in Kent: If left uncontrolled, then buddleia and other shrubs would have engulfed the chalk grassland. Clouds of butterflies used to be seen there, but now only common species can be spotted and even these are in decline, with the rarest ones disappearing altogether. Buddleia was eliminating butterfly habitat by killing off everything else, and while the shrub provided food for adults and larger insects, other plants were needed for butterflies in their larval stages.

So there you have it – it’s just like the human history of Ireland, full of invasions, adaptations, displacements and resurgence. All in a Wild Wall.