Senecio cambrensis

Senecio cambrensis (Welsh groundsel or Welsh ragwort) is a flowering plant of the family Asteraceae. It is endemic to the United Kingdom and currently known only from North Wales. It is a recently-evolved plant which arose suddenly as a result of hybridization between two related species.

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Origin

Welsh groundsel is an allopolyploid, a plant which contains sets of chromosomes originating from two different species. Its ancestor was Senecio × baxteri, an infertile hybrid which can arise spontaneously when the closely-related groundsel (Senecio vulgaris) and Oxford ragwort (Senecio squalidus) grow alongside each other. Sometime in the early 20th century, an accidental doubling of the number of chromosomes in an S. × baxteri plant led to the formation of a new fertile species, Welsh groundsel.

Distribution and habitat

It was first discovered in 1948 by Horace E. Green at Ffrith in Flintshire, north-east Wales. The species was described in 1955 by Effie M. Rosser of Manchester Museum using material from the site. It was later found at a number of sites across the north-east of Wales including Chirk, Brymbo, Queensferry and Colwyn Bay and a herbarium specimen was discovered which had been collected at Brynteg in 1925.

In England it was reported from Shropshire and an introduced population appeared in Wolverhampton. The Shropshire record is now thought to be erroneous and the Wolverhampton plants have disappeared. There are no recent records from England.

In 1982, Welsh groundsel was discovered at several sites around Edinburgh, Scotland. This population arose independently from the Welsh population; it is believed to date from at least 1974 but now appears to have disappeared with no records since 1993.

Typical habitats of the species include waste ground, roadsides and cracks in walls and pavements.

Description

The plant is intermediate in appearance between its parents, groundsel and Oxford ragwort. It is an erect annual plant which reaches a height of 30 (sometimes 50) centimetres. The stem and leaves have few or no hairs. The leaves are deeply lobed, the lower ones have stalks while the upper leaves are attached directly to the stem. The flower heads are cylindrical and usually have 8 to 15 yellow ray florets ("petals") although some are rayless. The ray florets vary in length but are most commonly 4 to 7 mm long. The pollen grains are 30 to 36 micrometres across and usually have 4 pores.

References

• Abbott R. J. & Forbes D. G. (2002) Extinction of the Edinburgh lineage of the allopolyploid neospecies, Senecio cambrensis Rosser (Asteraceae), Heredity 88, 4:267-269 (retrieved 15/02/07)
• Cheffings, Christine M. & Farrell Lynne (eds.) (2005) The Vascular Plant Red Data List for Great Britain, JNCC (retrieved 15/02/07)
• Ellis, R. Gwynn (1983) Flowering Plants of Wales, National Museum of Wales.
• Ingram, Ruth & Noltie H. J. (1984) Ray floret morphology and the origin of variability in Senecio cambrensis Rosser, a recently established allopolyploid species, New Phytologist 96: 601-607 (retrieved 15/02/07)
• Shropshire Botanical Society (2002) Shropshire Botanical Society Newsletter (retrieved 15/02/07)
• Stace, Clive A. (1997) New Flora of the British Isles, Cambridge University Press.
• Wynne, Goronwy (1993) Flora of Flintshire: the flowering plants and ferns of a North Wales county, Gee & Son.