Senecio squalidus L. (Asteraceae)


Oxford ragwort

Senecio squalidus on the walls of St. Peter's in the East Church, where the Bobarts and Dillenius are buried (May 2010; SA Harris). Hand-coloured metal engraving of Senecio squalidus from William Baxter's 'British Phænogamous Botany' (1834; t.52).

In the early eighteenth century, an unknown Sicilian plant arrived in Oxford; its precise means of admission unknown. However, it appears to have involved at least one Italian monk, a British diplomat with a botanical bent and an amiable personality, a dowager Duchess and Jacob Bobart the Younger, head of the Oxford Physic Garden. From Bobart's time until the early 1800s, Oxford ragwort was a novelty confined to the city's walls and a few parishes looked after by Oxford-trained prelates who wanted to remember their student days. The light, parachute-like ragwort fruits are effective dispersal units. Yet to be ecologically successful in its new home, Oxford ragwort needed time to adapt, suitable habitats to grow in and a means to escape to the rest of Britain.

The 1840s brought the railway, with its track ballast, to Oxford. Ragwort could escape its rarefied confines, take advantage of industrial disturbance, and spread through western Britain. After the Second World War, the destruction created by German bombs produced more habitats for Oxford ragwort and a second colonisation front was opened up in eastern Britain. Today, Oxford ragwort's distinctive, star-like, yellow inflorescences are a familiar feature of spring and early summer across Britain, wherever well-drained, man-made habitats abound.

The species' inappropriate Latin name was bestowed by Carolus Linnaeus, based on samples collected from the walls of the Physick Garden and apparently sent to the Swede by Professor Johann Jacob Dillenius in the 1730s. The first complete account of Oxford plants, published in 1794 by Professor John Sibthorp, failed to recognise the ragwort on the walls was that described by Linnaeus.

However, Oxford ragwort is more than merely a weedy plant that happened to leap a garden wall; it has evolved to become a model plant for studying the evolution of wild plant populations. Although crosses with our native groundsel (Senecio vulgaris) produce sterile hybrids, a few, following complex genetic changes, are fertile. In the last 150 years, three of these hybrids have been formally described as new taxa; radiate groundsel (Senecio vulgaris var. hibernicus), Welsh ragwort (Senecio cambrensis) and, most recently, York ragwort (Senecio eboracensis). We have discovered Oxford ragwort itself is a hybrid of two Italian species; one (Senecio aethnensis) endemic to the top of Mount Etna, the other (Senecio chrysanthemifolius) widespread in southern Italy. Although adaptation to English life was slow, the ragwort adapted to Scottish life in fewer than 50 years.

Further reading

Abbott, R.J. & Lowe, A.J. (2004) Origins, establishment and evolution of new polyploid species: Senecio cambrensis and S. eboracensis in the British Isles. Biological Journal of the Linnean Society 82: 467-474.

Allan, E. & Pannell, J.R. (2009) Rapid divergence in physiological and life-history traits between northern and southern populations of the British introduced neo-species, Senecio squalidus. Oikos 118: 1053-1061.

Harris, S.A. (2002) Introduction of Oxford Ragwort, Senecio squalidus L. (Asteraceae), to the United Kingdom. Watsonia 24: 31-43.

Stephen Harris