The Oxford Ragwort storyOxford ragwort ( Senecio squalidus), is a hybrid between two Senecio species native to Mount Etna in Sicily, Senecio aethnensis and Senecio chrysanthemifolius. It was introduced into the UK around 1690 via the Oxford Botanic Garden where it was grown by the Horti Praefectus Jacob Bobart. Following many years of cultivation in the Botanic Garden, S. squalidus 'escaped' and could be found growing in the masonary of Oxford colleges and walls (hence its common name of Oxford ragwort). By 1794 it was 'very plentiful on almost every wall in and about Oxford' wrote Professor of Botany, Sibthorp.
During the Industrial Revolution, Oxford became a thriving railway centre and Oxford ragwort found a new habitat in the clinker beds of the railway lines that fanned out of Oxford to all parts of the country. These "furnished the plant with a replica of the lava-soils of its native home in Sicily", said Druce in his Flora of Oxfordshire. Referring to the fruits (achenes) of Oxford ragwort, he said 'I have seen them enter a railway-carriage window near Oxford and remain suspended in the air in the compartment until they found an exit at Tilehurst' (near Reading). Since that time, Oxford ragwort, which should not be confused with the common ragwort (Senecio jacobaea), the well-known irritation of pony owners, has spread to most parts of the UK, where it favours disturbed habitats such as building sites, roadsides and railway lines (you will see lots of its yellow daisy flowers if you take the Great Western line to Bristol any time from May to October).
During its spread across the British Isles, Oxford ragwort has hybridized with other native Senecio species, particularly groundsel (Senecio vulgaris) to form new hybrid taxa, some of which have been recognized as new species because they have become reproductively isolated from their parents. For instance, hybridization with native groundsel on at least two occasions within the last 100 years, once in Wales and once in Scotland, has resulted in the new allopolyploid hybrid, Senecio cambrensis (via the infertile intermediate hybrid Senecio x baxteri). More recently, perhaps within the last 30 years, a different cross between an unreduced pollen grain of S. squalidus and groundsel formed the fertile hybrid Senecio eboracensis, which so far is limited to a few sites in the city of York. The discovery of this new species by Richard Abbott caused quite a stir in the media (see below). A third novel Senecio variety, Senecio vulgaris var. hibernicus or radiate groundsel, was formed by a backcross between Senecio x baxteri and S. vulgaris. S. squalidus has also hybridised with another native species Senecio viscosus, to form a mainly sterile hybrid Senecio subnebrodensis. Thus, the introduction and spread of the promiscuous Sicilian S. squalidus has resulted in a great deal of evolutionary novelty among British Senecio - an amazing example of evolution in action.