Oxford Ragwort Senecio squalidus is a common coloniser of railway tracks and sidings throughout the UK

Oxford 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. Distribution maps showing spread of S. squalidus throught England and in parts of Scotland and Ireland 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"