This yellow-flowered species arose in a famous university's botanic garden as a hybrid of two Sicilian species from the slopes of Mount Etna
Oxford ragwort - Senecio aethnensis x S. chrysanthemifolius.
Nature · Wildflowers & flowers
Oxford ragwort
Neophyte · flowers spring to late autumn, sometimes winter · walls, railways, waste ground
Senecio squalidus — Asteraceae
Oxford ragwort is a species that was born in a garden: a hybrid between two Sicilian ragworts from Mount Etna that stabilised into a new species in Oxford's botanic garden, escaped over the wall in the 1790s and then raced across Britain along the railways from about 1879. It thrives on cinders, ballast and pavements.
How to spot them
- ▸Loose clusters of bright yellow daisy-like heads 16-20 mm across, with about 13 ray florets, on a smaller, bushier plant than common ragwort
- ▸Glossy, deeply and pinnately cut leaves with narrow pointed lobes
- ▸Winter-green; sprouts from cracks in walls, pavements, ballast and rubble
- ▸Outer bracts at the base of the head have black tips
- ▸Look-alike: common ragwort is taller with flat-topped dense heads and blunt-lobed leaves; sticky groundsel has small heads and is sticky-hairy
How to know it
First recorded escaping the garden in 1794, it spread rapidly after reaching the railway around 1879, with cinder ballast suiting a plant of volcanic slopes
Oxford ragwort - BSBI; the volcanic-ash comparison is a popular explanation.
It is the textbook example of 'homoploid hybrid speciation', forming a new species without doubling its chromosome number
Oxford ragwort - it is diploid, 2n = 20.
A hybrid of this plant and groundsel produced a brand-new British species, discovered in a city on the Ouse in the 1970s
Oxford ragwort x groundsel gave York radiate groundsel, Senecio eboracensis.
A single plant may produce around 10,000 parachute-borne seeds, which is why it colonises pavement cracks and railway ballast so quickly
Oxford ragwort - BSBI.
A shorter, branched yellow 'weed' of walls and railways, told from the taller field roadside species by its finely cut shiny leaves
Oxford ragwort (common ragwort, Jacobaea vulgaris, is the look-alike).
Quick-fire facts
- •Introduced from cultivation: a neophyte (post-1500); family Asteraceae
- •BSBI: arose as a hybrid in the University Botanic Gardens, Oxford, between Sicilian Senecio aethnensis and S. chrysanthemifolius
- •Escaped into the wild in 1794; also recorded at Bideford, north Devon, before 1830
- •Dispersed very rapidly from about 1879 once it reached the railway network
- •Each plant produces about 10,000 achenes with a parachute of hairs (BSBI)
- •A textbook example of homoploid hybrid speciation - a rare event where a hybrid becomes a new species without genome doubling
- •Hybridised with groundsel to make York radiate groundsel (Senecio eboracensis), first found in 1979
- •Slower to spread in Ireland, where it remains rare and local (BSBI)
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Sources
- BSBI — Senecio squalidus L., Oxford Ragwort
- Royal Horticultural Society — Senecio squalidus (Oxford ragwort)