A descendant of Sicilian progenitors, this daisy-family plant appeared in the UK, escaped from a botanical garden, and began its conquest of the region during the Industrial Revolution.
It is rare to uncover the details of a story as fascinating as this, especially since there are few cases where the emergence of a new species can be traced across just 300 years. The Oxford ragwort, Senecio squalidus, a yellow-flowered plant from the daisy family, first appeared in the 17th century at the Oxford Botanic Garden after a crossbreeding of two plants native only to Mount Etna in Sicily.
Bruno Nevado, researcher at the Centre for Ecology, Evolution, and Environmental Changes (CE3C) at the Faculty of Sciences of the University of Lisbon (CIÊNCIAS), leads the study now published in the scientific journal Current Biology. The research reveals key moments in the existence of this species-from its origins to its colonization of the United Kingdom during the Industrial Revolution-through the lens of genetics.
Between the late 17th and early 18th centuries, Senecio chrysanthemifolius and Senecio aethnensis, plants endemic to the rugged slopes of Mount Etna in Italy, were introduced to the gardens of the Duchess of Beaufort in Gloucestershire, England, by botanists Francesco Cupani and William Sherard. On Mount Etna, these plants rarely mingled due to their distinct habitats - S. chrysanthemifolius at altitudes below 1,000 meters and S. aethnensis above 2,000 meters. However, in the UK, conditions brought them into closer proximity, resulting in hybrid individuals. By the first two decades of the 18th century, these hybrids were cultivated in the renowned Oxford Botanic Garden, where they eventually gave rise to a new hybrid species, Senecio squalidus (hence Oxford ragwort). By the end of the 18th century, S. squalidus had escaped its confines and spread into the urban environment of Oxford, beginning its naturalization and eventual colonization of the UK.
Possibly due to its descent from species adapted to the harsh volcanic landscape, this hybrid species managed to thrive, later spreading via the expanding railway network of the Industrial Revolution in the 19th century. It was "by train" that the yellow flowered Oxford ragwort reached nearly every corner of the UK over a span of 150 years. Today, the species can be found from Scotland to Wales, and even in Ireland, thriving along railway lines, roadsides, footpaths, industrial zones, and other disturbed habitats.
Senecio squalidus is one of a few hybrid species with a very recent origin. Bruno Nevado highlights this rarity: "Normally, hybrid species are much older, and it's difficult to disentangle the processes that contributed to speciation from those that affected the hybrid species later on during its evolution. But with this species, we can study the processes involved in the very early stages of speciation".
In this new study, conducted in collaboration with researchers from several British universities and the Wellcome Sanger Institute in Cambridge, the genome of S. squalidus was sequenced. Genetic analysis of both S. squalidus and its parental species revealed a rapid reorganization of the hybrid species' genome, driven by the resolution of genetic incompatibilities between the parental species and natural selection. These processes shaped a unique genome, combining traits from both parents, allowing the new species to thrive in an environment where neither parent could survive. Thanks to this unique evolutionary journey, "The Oxford ragwort serves as a small, exceptional laboratory for studying hybridization and its role in the emergence of new species and the colonization of challenging environments," concludes Bruno Nevado.
