Taxonomy

Senecio cambrensis Rosser, Welsh Ragwort, evolved when an infertile hybrid between S. vulgaris (Groundsel) and S. squalidus (Oxford Ragwort) underwent chromosome doubling. The new species was first found in 1925 and was formally described by Effie Rosser in 1955 (Ashton in Wigginton 1999; Killick in Preston, Pearman & Dines 2002). Genetic evidence points to at least two and possibly three separate evolutionary origins (Ashton & Abbott, 1992).

Identification

It is easy to confuse with S. squalidus and with rayed forms of S. vulgaris. The length of the achene and the flask-shaped capitulum are useful characters for distinguishing it (Stace, 1997).

Distribution

It is entirely restricted to north Wales. A population that occurred in Edinburgh, which has been shown to have arisen independently, has now died out (Abbott and Forbes, 2002).

Some maps show dots elsewhere in Britain, Wales and Scotland, but these are all apparently either mistakes or deliberate and temporary introductions to gardens (data from the TPDB).

Ecology

It is typically an annual, germinating in spring or autumn and flowering from May to October. It occurs in disturbed sites such as rubble, gardens and thin soils alongside roads. Senecio squalidus, S. vulgaris, Sonchus oleraceus and Taraxacum species are commonly associates. (Ashton, op. cit.). No NVC communities have yet been described for it.

Status

This is the only species of vascular plant that is entirely confined to Wales (if you ignore a few microspecies of critical taxa). It has evidently failed to spread significantly since it was discovered, although Chirk appears to have a healthy population. It appears from the Maps Scheme maps and personal observation to have declined somewhat in the last twenty years, partly through loss of habitat following post industrial development and possibly also from change in management regimes of roadside herbicide treatments.

It is listed as Near Threatened by Cheffings & Farrell (2005), but if it is declining as much as is shown by the Maps Scheme, it may be more vulnerable than this suggests

Further work

Due to the extensive research work undertaken by Richard Abbott and various co-workers it has become one of the classic examples of rapid plant evolution (see Lowe et al., 2004 Chapter 7.3 for a fuller overview of the evolutionary processes of this and related species). Given that both parental species are widespread and sympatric the possibility of it arising elsewhere should be borne in mind.

This is not a plant of any great ecological significance. However it would be useful to continue to survey its populations regularly to see if it responds to its changing environment. Specifically regular monitoring to distinguish the population fluctuations characteristic of annual species from long term population trends would be very useful. All records need to be backed up by good quality photographs or voucher specimens, as it is very easy to confuse this species with its close relatives.

Plants are often infected with the rust Puccinia lagenophorae (det. Nigel Stringer), which could possibly threaten its viability, although this rust is common on its parental species. Observations on such threats and the vigour of populations might provide useful insights.

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References

Abbott, R.J., Ingram, R. & Holtie, H.J. 1983. Discovery of Senecio cambrensis Rosser in Edinburgh. Watsonia 14, 407-408.

Abbott, R.J. & Forbes, D.G. (2002). Extinction of the Edinburgh lineage of the allopolyploid neospecies, Senecio cambrensis Rosser (Asteraceae). Heredity 88: 267–269.

Ashton, P.A. & Abbott, R.J. (1992). Multiple origins and genetic diversity in the newly arisen allopolyploid species, Senecio cambrensis Rosser (Compositae). Heredity 68: 25–32.

Lowe, A. Harris, S.H. and Ashton, P.A., (2004) Ecological Genetics: Design, Analysis and Application. Blackwells Oxford

Acknowledgements

Account by Paul Ashton

Photographs by Alex Lockton