Senecio eboracensis, 18th March 2024 (York Radiate Groundsel)

In 1979, a plant scientist named Richard Abbott parked his car in an unremarkable car park in the city of York, where he and his student were soon examining a healthy population of what looked like radiate forms of the common groundsel (Senecio vulgaris).  However, as he sat down to lunch beside the population, Richard noticed the distinctive features of the plant and immediately recognised its significance, which had evaded the attention of a number of local botanists.  With growing excitement, he began to wonder if this find was something new?

Richard Abbott, in 2023 with a batch of York Radiate Groundsel (photo courtesy of Richard’s family)

Throughout the 1980s and 1990s, Dr. Abbott investigated this strange new plant, which he informally named the York Radiate Groundsel.  He and his team counted the chromosomes, and tested how inter-fertile it was with similar looking plant species.  By the early 2000s, it was clear that this was a species new to science, and Dr Abbott described it as such with his former student Andy Lowe.  They gave it the name Senecio eboracensis, using the old Roman name for the city of York.  By this time, the species had spread a little, and I recall finding it on the stone banks of the river near the city centre. 

The discovery of a completely new plant species within the British Isles, and especially in such an unlikely setting, generated interest in the UK national media.  Headlines along the lines of “Scottish scientist finds new species in car park” also caught the intention of light-hearted panel shows, including Radio 4’s The News Quiz, and BBC1’s Have I got News For You.  On the former, the much-missed comedian Linda Smith poured light-hearted scorn on the story.  I can’t recall her exact words, but it was along these lines: “I must say, these Scottish scientists have gone downhill a bit over the years.  I mean, Alexander Fleming, penicillin, hats off!  But now they’re grubbing around in car parks looking for weeds.”

The York Radiate Groundsel Senecio eboracensis (Photo: Andy Shaw at the Rare Plants Nursery, Wales)

Of course, there was much more to the story than this.  Where had the York Radiate Groundsel come from?  In fact it was the product of not one but two extraordinary evolutionary events, and owed its existence to both natural events and human activity.  Its story started on Mount Etna, where two Senecio species grow naturally, one at the top (where it is endemic) and one at the bottom.  The construction of a road up the mountain allowed the two species to meet, because the disturbed ground by the roadside proved suitable for both of them, and soon they formed large hybrid populations, with great variation in form.  These caught the eye of botanists, who carried the hybrids back to Oxford botanic garden, where they existed in cultivation for many generations.  During this period natural selection was able to act, acclimatising the population to the UK climate.  Hybrid populations contain far more variation than normal plant populations, and selection kept those bits of DNA that best suited its new environment, dispensing with the rest.  In this way, the initially highly variable hybrids stabilised into a stable species, which we now know as the Oxford Ragwort, Senecio squalidus.  After a while, S. squalidus escaped from Oxford Botanic Garden and found its way onto a nearby railway track, just as the age of steam train travel was hitting its peak.  Steam-blasted railway ballast proved a perfect habitat for a plant whose recent ancestors had lived on a volcano, with the added benefit that passing traits were extremely efficient at carrying the feathery seeds along railway lines.  In this way, the species spread like a rocket across most of the British Isles, becoming a familiar member of our flora. 

The common Groundsel in its typical (left) and rayed (centre) forms, and the Oxford Ragwort (right).  These two species were shown to be the parents of the York Radiate.  Photo Richard Milne

Occasionally, hybrids between S. squalidus and S. vulgaris managed to back-cross with another S. vulgaris plant, to give offspring with the same chromosome number as S. vulgaris.  When successive generations repeatedly back-cross in this way, the effect is to progressively dilute the genetic influence of one species, either down to nothing or just a very few genes.  This is how ray florets got transferred from the Oxford Ragwort to created rayed forms of Groundsel, which are sometimes seen around Britain, and as far afield as Tenerife. 

The Oxford Ragwort, Senecio squalidus, pictured in Tenerife (photo: Richard Milne)

As with the York Radiate, it was Richard Abbott who led the research on unravelling this story, and indeed on the stories that follow, because that was only Part One.  As it spread around Britain, S. squalidus came into regular contact with the common groundsel, S. vulgaris.  The former is showy and colourful, as befits a plant which uses pollinators to breed sexually.  The groundsel, by contrast, is usually self-pollinating and so has dingy flowers with no ray florets, looking superficially very different.  But the two were capable of producing very occasional hybrids, albeit with very low fertility because the Groundsel has twice as many chromosomes as the Ragwort, which generally leads to sterile offspring.  On two occasions the resulting hybrids solved this problem by doubling up their DNA, and so containing the complete genomes of both parent species, forming the polyploid hybrid species Senecio cambrensis.  This happened first in Wales (hence the name) and later in Leith, Edinburgh, though the latter population sadly died out.  The Welsh population is also sadly declining, losing its favoured roadside habitats to herbicides and salting.

The origin of The York Radiate, meticulously worked out by Drs Abbott and Lowe, fell somewhere between these two processes.  It has the same chromosome number as the Groundsel, and is closer to it genetically, but is perhaps 20 to 40% Oxford Ragwort (compared to the standard radiate groundsel which has less than 1% ragwort).  Andy Lowe describes a moment when Richard Abbott observed a population of natural hybrids between Groundsel and Oxford Ragwort in Ireland, and Richard literally danced for joy when he found individual plants that looked like the York Radiate mixed with a wide range of hybrids (called a hybrid swarm), demonstrating that plants with this combination of traits could arise by hybridization (Richard soon paid for his exuberance because his car keys fell from his pocket, necessitating a long search).  From this, it seems clear that similar hybrids were once produced in York, after which selection kicked in, casting aside unsuccessful forms and narrowing down the hybrids into something new and stable – the York Radiate.  In fact, Abbott and Lowe were also able to recreate this process in the glasshouse, and long searches through herbarium sheets showed that hybrid swarms had existed in many cities around Britain during and since World War 2 (Bristol and Cork in particular).  But in the wild, as far as we know, the full process to establish a pure-breeding, stable, hybrid species only ever happened once – in York

The York Radiate Groundsel Senecio eboracensis (Photo: Andy Shaw at the Rare Plants Nursery, Wales)

So, the Oxford Ragwort and Groundsel produced an astonishing three different evolutionary entities, but how does one tell them apart?  Compared to the York Radiate, the rayed forms of Groundsel have shorter (<2.5 mm) achenes, and the Welsh Groundsel usually has more than nine rays per flower (and has never been found near York).  However the presence of at least 13 leaf lobes should distinguish the York Radiate from either.  All three have narrower flower heads than the Oxford Ragwort.

After its initial discovery in 1979, the York Radiate appeared to enjoy a period of spread, increase its range within the city, though it never spread outside it.  Hence my own happy encounter with it on the river wall in the 1990s.  Sadly, ‘progress’ then took a hand.  Brownfield sites were redeveloped, and that annoying human desire for neatness in outdoor spaces led to increased herbicide use to remove “unsightly weeds” from places like car parks.  The York Radiate was lost from the wild by 2003.

Happily, this was not the end, for seeds had been preserved in Kew’s Millenium Seed Bank, and in 2022 these were passed to the Rare Plants Nursery in Wales, where a thriving cultivated population was rapidly generated.  From these, reintroductions were made around York in 2023, and the York Radiate once again flowered in the city later that summer.  It is to be hoped that those who run the city now understand that the York Radiate is as much a part of the city’s heritage as Vikings, the Roman city wall, and York Minster.  What other city can boast a wild plant that quite literally evolved there and has never occurred anywhere else?  I spent a happy afternoon doing a treasure hunt around the city centre with my brother’s family, and those who made it would be missing a trick if they didn’t create a “find the York Radiate” botanical treasure hunt this summer.  Of course, visiting botanists can – and should – do this for themselves.

Reported from York, 5th June 2023, by Alex Prendergast who said “Several patches of York Groundsel Senecio eboracensis seen about the city on my way from the station this evening. Most drought stressed and small. Some lost to drought. Luxuriant growths nobbled by the weedkiller brigade. But 20 or so plants in flower without really looking”. Reproduced with Alex’s permission.

Professor Richard Abbott passed away earlier this month at the age of 79.  Though the York Radiate must have arisen some time before he discovered it in 1979, it seems almost certain that this species arose, spread, and then declined to extinction, all within the lifespan of its human discoverer.  Like human beings, species have finite lifespans, although biologists estimate that around 5 million years may be a more typical length of time on earth for a plant or animal species.  If we leave aside its anthropogenic second coming and consider only its period of unaided existence in the wild, the York Radiate becomes one of the shortest-lived species ever recorded, with a natural lifespan of just 24 years, which is 200,000 times shorter than the supposed average. A human equivalent would be a baby that lasted just a quarter of a day.  Had its existence not coincided with that of keen-eyed botanists, it would have slipped in and out of the world entirely unnoticed. 

Andy Lowe at his PhD graduation party, decorated with S. eboracensis plants

This raises the question, have there been countless other ephemeral species like this, evolutionary experiments that came and went in the blink of an eye?  Some, perhaps, which arose and briefly thrived before a predator or pathogen learned to exploit them and wiped them out, but even those would probably have lasted longer than 24 years.  However, the human era – now increasingly termed the Anthropocene as an acknowledgement of how our species is affected every aspect of the biosphere – is unique.  The Oxford Ragwort arose because humans transported hybrids from Mount Etna to Britain, cultivated them, and build railway lines which they used to escape and spread across Britain.  Later its offspring with the Common Groundsel, the York Radiate and the Welsh Groundsel, both arose and adapted to manmade habitats.  One might also mention the Interrupted Brome, Bromus interruptus, which arose by mutation and for a few decades was a perfectly adapted weed of Sainfoin fields, before the crop went out of fashion, and this together with more efficient farming drove the species to extinction in the wild (again, it survives in cultivation).  

Senecio eboracensis on the south bank of the River Ouse in York. Photo: Alison Jukes

Never before have so many changes in the world occurred simultaneously over a sustained period, creating both habitats for new species to exploit, and opportunities for hybridization to create them.  But at the same time, even as we create new habitats, we then go on and change them.  Redevelopment in Leith, herbicides and salting on Welsh roads, agricultural ‘improvements’, and the war on weeds in York, can turn perfect conditions into hostile ones, within just a few years.  So perhaps the ultra-short lifespans of the York Radiate and the Interrupted Brome really were exceptional.

The York Radiate reminds us that human activity can both create and destroy.  It tells us that evolution on our planet is increasingly entwined with the human story, whether we want it to be, or not.  It also shows us that great scientific discoveries can be made at any time, in any place, provided we keep our minds and eyes open.  And its continued existence makes it a tribute to the man who discovered it, without whom it might have passed from existence without ever being noticed.

More images received from Alex Prendergast, all showing the plant growing wild in York.

Acknowledgements

Photos of York Radiate Groundsel courtesy of Andy Shaw at the The Rare British Plants Nursery, Wales, Alex Prendergast of Natural England and Alison Jukes. Thanks to Prof. Andy Lowe for contributing photos and narratives for this blog.

You may watch Richard Abbott’s lecture, given at the Urban Flora conference last year, here.

©Richard Milne