Dear Readers, I have long wondered why it is that some of our most successful urban ‘weeds’ are those that come originally from alpine regions (those between the treeline on a mountain and the upper limit of vegetation). Whilst most of the ‘weeds’ that I’ll talk about here also come from the Alpine region (i.e. in the European Alps), some of them come from mountainous areas on other continents. Interestingly, as far as I know none of our native alpine species have made the transition to urban life, but let me know if you can think of any examples. The plants below have mostly come into the UK as garden plants, but have made their way off the rockery and onto our walls with great enthusiasm.
For example, yellow corydalis (pictured above) comes from the foothills of the Alps in Switzerland and Italy. This attractive plant, a member of the Fumitory family, is the twelfth commonest ‘weed’ to be found on urban streets.
Trailing bellflower comes from the Dinaric Alps in the former Yugoslavia.
Ivy-leaved toadflax is found all over the Mediterranean, but has a great fondness for the Southern Alps.
And then there’s Buddleia of course, from the foothills of the Himalayas.So, what do they have in common? There are a number of things that make some mountain plants well adapted for life in the big city. Firstly, they have to be able to withstand exposure to a lot of light and wind. Secondly, they have to be able to manage in thin pockets of soil. Thirdly, they need to be able to withstand the drought that often happens in a place with non-permeable surfaces and not a lot of available water. And finally, in order to persist, they need to find a way to reproduce that enables future generations to survive.
Let’s have a look at these plants in turn. Yellow Corydalis is nearly always found growing on walls in London – I have a splendid example nearby, where the yellow of the plant often offsets the yellow of the graffiti. However, I often wondered how come it ended up there. My Alien Plants book by Stace and Crawley points out that the seeds of yellow corydalis contain something called an oil-body – this is irresistible to black ants, who gather the seeds and take them back to their nests. Often the ants have nests behind crumbling brickwork. They eat the oil body, and then the plant germinates in the nest, presumably busting through the mortar. I imagine that yellow corydalis has a similar relationship with the yodelling, clean-living ants of the Alps, and it finds that the niches in the tatty walls of Kentucky Fried Chicken remind it of the gaps between the rocks in its mountain home.
Trailing bellflower is another mountain specialist, and has again taken to our walls with gusto. It was only introduced to our gardens in 1931. By 1957 it had been recorded in ‘the wild’, and now it is even commoner on our London streets than yellow corydalis. It has a low-growing, straggling habit which protects it from the scouring mountain winds, and as it inches along the gaps between the brickwork in search of moisture and rootholds, I can just imagine it doing the same in the Dinaric Alps. It loves the stone steps of the Victorian homes here in East Finchley, and in Islington it popped up in the Georgian basements.
Ivy-leaved toadflax is a favourite plant of mine: I love the three-lobed flowers, and the way that the plant thrives in such hostile places. There is a fine collection on a very run-down wall locally, much favoured in the old days by men who were ‘caught short’ after a few too many pints and felt obliged to water it.
Ivy-leaved toadflax is another very successful muraphile (‘wall-lover’, though I think I might have just invented a word). It reproduces both by stolons (long stems that spread out from the mother plant and take root when they find moisture), and by seed. The flowers grow towards the light until the plant is pollinated, but once the seed matures, the flower turns and points downwards, so that the seed will hopefully drop into a moist niche in the wall. What many of the successful mountain ‘weeds’ have in common is the ability to maximise the chances of their offspring’s survival, whether by finding a damp place to pop the seeds or persuading ants to take them away.
And finally, that most successful and flamboyant of mountain ‘weeds’, the buddleia. In Alien Plants, Stace and Crawley remark that the buddleia is one of those rare plants that has found a ‘new’ niche for itself – the gaps between the bricks in urban buildings, not at street level but high up. I well remember noticing a buddleia that had seeded itself some thirty feet above the ground, on the grimy walls that led into Liverpool Street Station. It had grown into a substantial bush while gripping on to what must have been the tiniest of recesses. While all of our plants have managed to make a living on walls, none takes it to the extreme that buddleia does. It generally seems to love the railway lands, which remind it of the scree slopes of the Himalayas where it originated, and on a trip to Dorset I used to love to see the forests of buddleia as they advanced along the sidings, the airy-light seed having been blown there by every passing train.
Buddleia is superbly adapted to city living – watching the one outside my window being blown almost horizontal by the wind without breaking, I can see how it can hang on even when the substrate is very thin. It produces a veritable sandstorm of pollinated seed, both because it is so popular with insects and because the flowers are perfect, containing both male and female parts, and so the plant can self-seed (something that yellow corydalis does too). And here, a quick word about buddleia’s value to wildlife – although we all know about the popularity of the flowers, it has recently been noted that the caterpillar of the Mullein moth (Cucullia verbasci) sometimes feeds on buddleia as well, which will be a relief if you’re trying to grow verbascums. What a magnificent caterpillar, though and, if the comments from my gardening friends are anything to go by, it’s having a very good year.
So, the alpine plants that have made the switch to city living seem to have a number of things in common: they thrive on exposure and thin soil, they have switched from rock-crevices to walls, they have seed mechanisms that increase the chances of the next generation, and they can survive drought. However, not every alpine plant is able to survive in the harsh world of the city: I don’t see gentians popping up (unfortunately) and I’m not tripping over edelweiss. Many alpine plants are slow-growing and extremely specialised, growing in tiny microniches. In all my years in the Austrian Alps, I have never seen the aforementioned edelweiss growing in the wild, because it likes rocky limestone above 3000 metres, it has no tolerance for disturbance or pollution, it is always scarce, and it is also extremely short-lived. It has grown a coat of hairs to protect it from the cold, aridity and exposure of its chosen habitat, and has become the symbol for rugged alpinism. I admire the alpine species that are all around me in North London, whilst recognising the precarious foothold that plants like the edelweiss have in their native lands. How vulnerable these extreme mountain specialists are, living on the very edge of what is possible. As global heating changes their environment, they will have nowhere else to go.
Photo One By Noebse – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=51991998
Photo Two By Bobr267 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=61678532
Photo Three By Böhringer Friedrich – Own work, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=11882229