Nature 2014 August

The natural history of the Cosa Nostra’s invasion of the British Isles

There is a small assortment of wild plants in Britain that have made their mark by taking advantage of changes in landscapes, usually through man’s activities. Each have their own unique, often bizarre, story. Here is the story of just two to whet the appetite.

I recall growing up in London in the post World War II era and like many who lived in cities and large towns across will the UK can remember the large number of bombsites which were left in ruins, in many cases throughout the fifties into the early sixties. I also recall they were excellent places to visit to discover interesting butterflies and moths. For many it was not until major inner city investment commenced and resulted in the development of high-rise residential or of new industries forged in Harold Wilson’s ‘white heat of technology’. One of the first invaders of these derelict oases was a new urban dweller. Not human, not animal, but a perennial plant we know as Rosebay willowherb. It first came to prominence in our cities around 1940, a matter of weeks after the start of the Blitz. Not unsurprisingly then that it acquired the colloquial name of ‘Bombweed’. However, World War Two was not the first time a rampant invasion by this plant had been observed as a consequence of a World War. What appears to be a sudden invasion of an otherwise innocuous and colourful plant was almost the concluding stage of a much longer-term infiltration into a wide range of habitats.

Up until the end of the 17th century it is thought it was absent from the wild habitats of Britain. Though recorded by some herbalists of the time this is probably more down to confusion with a related species which resulted in it being labelled as ‘Codlins-and-cream’. Codlins is an Old English name for cooking apples and the name is on account of the similarity to ripe apples of the colour of the pink and off-white flower spikes of the closely related Great willowherb. During the late seventeen hundreds individual plants found were possibly the result of garden escapes

One of the earliest records of this plant in the wild was compiled by the early antiquarians during their archaeological investigations on ancient ruins, Not in Britain but across Mediterranean Europe, where it was found bursting out of crevices in the remains of ancient Roman and Greek buildings in Italy. One of the first to bring some back to Britain were probably some travellers to southern Italy possibly Sicily. This might have been either accidentally or on purpose, amongst their collections of artefacts. Known then as ‘French Willow’, it soon came to the attention of seventeenth century gardeners. Despite more frequent escapes from landscaped gardens into the countryside it remained relatively scarce well into the 19th century when it began to be found expanding its territory. Botanists considered it a rare but determined opportunist in the Home Counties and Midlands. This all began to change at the start of the 20th Century. At the time its progressive appearance was not understood. However, historians have concluded its increasing appearance in forest plantations, woodlands and heather moorlands was not a natural occurrence. Rather, during the first decade of the 20th Century the British Army began a large-scale rearmament in preparation of war with Germany. Large tracks of woodland were felled to supply timber for military purposes. Moorland was cleared of heather and planted with coniferous trees. This transformation of our managed landscapes continued apace during the First World War. After clearance the remaining ‘stocklands’ (areas comprising just tree stumps) were deliberately cleared by burning to enable rapid replanting. However in the interim period when trees had been removed the willowherb spread relentlessly. Not surprisingly, for this reason in the US and Canada it has another name ‘Fireweed’ due to its ability to be the first coloniser of newly fire-damaged forest areas. It is even incorporated into the Yukon Territory flag.

The success of Rosebay willowherb is down to the explosive nature of its seed dispersal. The average plant produces around 80,000 seeds each year. Each seed has a plume of hairs which create an aerodynamic parachute capable of transporting the seed over many miles in the lightest of breezes. En masse seed dispersal of large colonies of willowherb are known as blizzards, as the nearby trees and grassland can become clothed in a whitewash of seeds. The hairs prove useful in attaching to animals, (including horses and their mounts along woodland rides). As the seeds can remain dormant but viable for many years it is ideally suited to exploit an opportunity after a severe fire, explosion, or other disturbance.

The second plant with an intriguing story is Oxford ragwort. Like its close relative, Common ragwort, it has bright yellow daisy-like flowers. Though a different tale from that of willowherb, coincidentally its story also starts in Italy where it was first recorded in 1701 growing only on well-drained rocky ground, typically the eroded volcanic larva of Mount Etna in Sicily.

It was brought back to England and shortly after ended up at Oxford’s Botanic Garden. It was subsequently classified by Linnaeus from specimens sent to him from Oxford, noting that unlike related species, its habitat was tightly restricted to poor soils comprising mainly rocks. It was originally known as ‘Sicilian ragwort’ actually a hybrid between two species both found in Sicily . By the 1800s though the plant had escaped the confines of the botanic garden in all directions, it was almost exclusively to be found, on the tops of the old walls of the city, growing out of crevices in the buildings of certain Oxford University buildings and in particular favoured the Bodleian Library.

Around 1830 the Great Western Railway arrived in Oxford and very shortly afterwards the ragwort was to be found growing on the tracks at Oxford Railway Station. Within a few years this herbaceous plant had spread up and down the railway line but was restricted to growing out of the granite chips and clinker that made up the ‘permanent way’. A plant can produce up to 10,000 seeds per season, each with their own umbrella to catch the wisps of wind or in this case be caught up in the slipstream of passing steam engines. A chronicler in the 19th century described how some seeds got into the carriage with him at Oxford Station and travelled all the way down the line to Tilehurst where they alighted. Others wrote of finding specimens appearing at further and further distances from Oxford ending up in Penzance and into South Wales, then later spreading up from Abergavenny all the way to Hereford where it met up with those travelling up north from Oxford. From here it reached North Wales all the way to Holyhead. At the same time it also spread outwards to be found on waste ground for up to half a mile either side from the track bed. By the end of the Second World War it was also found growing on bomb sites. Oxford Ragwort reached the Scottish Lowlands in the 1950s and with the advent of the motorway network in the 1960s the plant was able to rapidly spread along the newly granite-strewn scarps and verges. In 1979 it was found for the first time across the Irish Sea, on waste ground beside a main street in Dublin. Possibly the boat-train from North Wales had been its courier? Though from a botanical perspective the plant provides an interesting story it should also be remembered that it is a serious hazard to livestock and needs to be eradicated from fields where horses or ponies might occupy or stray into.

As an interesting postscript to this essay, I found a brief comment which Richard Mabey wrote in 1996 in his Flora Britannica that (by the 20th century) that Oxford ragwort ‘now brightens all the waste grounds it graces, especially in the company of Rosebay willowherb’.

Two members of the ‘Sicilian Mafia’ that have made our countryside and towns their home.

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