Listen to this article
Plants are tenacious. It is one of the reasons why they have managed successfully to occupy most of the terrestrial Earth and a reasonable bit of the sea. Their tenacity enables them to cling on to life wherever they are, from precipitous mountainsides to desolate moors, steaming jungle to arid desert. Plants are great opportunists, too. Allowed the space and conditions to colonise, they invariably will; for every ecological niche there is a species waiting to fill it. Our road networks provide plants with numerous ecological niches and the perfect mechanism for dispersion; a network of corridors connecting distant places ripe for exploitation.
Just how niche such a niche might be is perfectly illustrated by the story of the sea fern-grass, Catapodium marinum. A low-growing plant, sea-fern grass lives in the moderately nutrient rich, brackish soils found in certain coastal regions. During summer it produces white flowers held on red flower spikes, although the flowers are so diminutive they are hard to spot unless you know what to look for. It isn’t especially common – in Europe it’s found no further north than the Netherlands – and frankly, it isn’t particularly exciting to look at. But it is tenacious. And, so it proves, it is also a great opportunist.
Late last year, Anne Appleyard of Wiltshire Wildlife Trust discovered a plant of sea-fern grass growing on a grass verge by the side of the A30 trunk road near Thorny Down, Salisbury. Appleyard had been looking at the flora of the verge banks, and in particular the young junipers growing there, when she spotted something unusual growing near the top of the kerb. It was small, shrivelled and brown but the sharp-eyed volunteer plant recorder recognised it and, after checking with the county recorder for plants, had it confirmed as Catapodium marinum. All of which would add up to not much of a story at all, except that the verge at Thorny Down is 40 miles from the sea.
How this plant came to transport itself so far from home is due to the opportunities afforded plants by human transport links. The verge is open and sunny, just the way Catapodium marinum likes it, and the granite kerb a reasonable facsimile of the pebble beaches the plant thrives on. The proximity to the roadside means that the ingredient not normally found 40 miles inland – salty, brackish soil – is plentiful thanks to the regular winter dosing of de-icing salt. So the sea-fern grass has gradually migrated inland, following in the salty slipstream of winter gritting trucks.
Appleyard believes there may be plants further inland as yet undiscovered. The fast moving traffic of a major road makes a fairly intimidating environment for botanising. If there are more colonies or brave individuals of Catapodium marinum, they would be trailing in the wake of another nondescript seaside plant that has exploded across the UK road network in the past four decades.
The charmingly named Danish scurvy grass was once a rarity inland, found on the occasional stretch of railway where ballast from the seashore had been deposited. It began to appear on major roadways from the late 1980s, on some roads spreading at a rate of up to 15 miles a year, the seeds whipped up by the air turbulence from passing vehicles and deposited in the salt laden roadside. It can now be found across the UK, especially on the central reservation and at the gritty, well-drained edges of verges. For most of the year it would be impossible to spot from the windows of a fast moving vehicle, but in early spring it blooms, a profusion of tiny white flowers forming an almost endless mat like the salt crust on a baked cod.
Salt doesn’t have to be a constituent ingredient in these roadway ecosystems. Along the stretch of Highway 1 that hugs the dramatic coastline through Big Sur, California, great swaths of the hummingbird’s trumpet (Zauschneria californica) can be found. Producing vibrant orange-red flowers in late summer and well into the dry west coast autumn, it gets its common name (another is the Californian fuchsia) from the hummingbirds that flit from bloom to bloom, and that are a primary pollinator. It seems to favour in particular the piles of fast draining road-stone that have been left behind from past road improvement schemes and that form long mounds, tilted west toward the baking sun. Zauschneria is supremely adapted to such thrifty “soil”. Its leaves are covered in fine, downy hairs that capture and absorb moisture from the thick fog that periodically rolls in from the Pacific during summer.
It is not just botanically curious natives and showy wildflowers that have taken to our transport systems. Decades of casually discarded apple cores, tossed from the windows of fast moving vehicles, have led to many British trunk roads becoming unofficial orchards. The vast majority of apple cores fall on barren ground and at the wrong time of year for seed germination, but if conditions are right germination can take place. Mature trees are a distinctively beautiful feature of motorways and A roads – especially in late autumn and early winter when heavy with fruit.
They are also an important genetic resource. Commercial apple trees are raised using vegetative techniques, by grafting on to a rootstock. The trees arising from discarded cores are genuine wildings, each one unique and with the potential to contribute their characteristics back into the apple gene pool, should the hybrid grafted plants become prone to pests or disease. The story of grape phylloxera illustrates just how devastating this could be; the tiny bug almost destroyed the French wine industry in the mid-1800s. The discovery that American grape vines had evolved natural resistance to it (the root stock of some American vines exudes a sticky sap that deters the nymph stage of the bug) resulted in French vines being grafted to American rootstocks. Wildings aren’t solely a phenomenon of British roadsides, or restricted to apples: wherever seed fruit is eaten and discarded, wildings can be found.
For an apple wilding to reach maturity it needs to dodge the periodic ravages of road verge maintenance. The sea-fern grass at Thorny Down was lucky; it was there to be discovered thanks to the existence of the Protected Road Verge Scheme, a partnership between Wiltshire Council and the Wiltshire and Swindon Biological Records Centre. The scheme has been in existence since 1975 and now covers more than 50 verges of special habitat, species or ecological interest, with each verge monitored by a volunteer, like Appleyard, feeding data back to the records centre.
The protection given to verges in Wiltshire is not, however, universal. Plantlife, the UK charity that lobbies for the protection of wildflowers, has launched a campaign to raise the profile of road verges as a significant bastion of wild plants and genetic diversity. British wild flower meadows have declined by as much as 98 per cent since the 1930s, and for many species the roadside verge offers an ecological niche that is a close facsimile to the species-rich grasslands they would have once called home. As a consequence, there are significant colonies of rare plants such as pyramidal (Anacamptis pyramidalis), bee orchid (Ophyrs apifera) and thistle broomrape (Orobanche reticulata) growing within an apple core toss of some of our busiest highways.
Plantlife’s campaign is aimed at trying to convince local authorities to revise their maintenance methods to prevent the verges being damaged or destroyed. At the most basic level, they hope to stop the senseless mowing of verges between March and August, which often results in plants being mown down just as they are about to flower. The charity has a job on their hands; so far only two authorities have signed on (hats off to Dorset and Poole) with over 250 yet to persuade.
When so much biodiversity is at threat from human intervention it is striking that the roadside verge has become the poster boy for wild flower conservation. The unique mix of endemic wildflowers, introduced wildings and translocated natives makes for a heady ecological brew that must be worth preserving.
Matthew Wilson is managing director of Clifton Nurseries, London
Get alerts on Gardens when a new story is published