Senecio cambrensis

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).

Chromosome No.: 2n = 60 (Stace 2010).

Senecio cambrensis

Photography: A.J. Lockton

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). 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. 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).

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

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 
  • Origin: native to Wales (and previously to Scotland).
  • Rarity: very rare. This is the only species of vascular plant that is entirely confined to Wales (if you ignore a few microspecies of critical taxa).
  • Threat: 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.
  • Conservation: it is not listed as an axiophyte in any county, given that its habitat is not of any importance.
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.

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
Citation 
Ashton, P.A. (Date accessed). Species account: Senecio cambrensis. Botanical Society of the British Isles, www.bsbi.org.uk.

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