Senecio squalidus L.
Oxford ragwort is an introduced annual to short-lived perennial weed of waste ground, walls and waysides. It occurs as a casual on arable land but is absent from grassland. It originates from Sicily where it occurs on volcanic soils. Seed from plants growing at Oxford Botanic Gardens escaped, hence its common name. It was first recorded in Oxford in 1794 and was considered plentiful by 1833. Oxford ragwort spread rapidly and is now common in England and Wales. It is not recorded above 300 m in Britain. Winter temperatures are higher in build up areas and this may favour its occurrence in urban areas.
Oxford ragwort flowers from May to December. The flowers are insect pollinated and self-incompatible. Seed is set from June onwards. The average seed number per flower head is 79 and the average per plant is 10,000.
Some seeds have a light requirement for germination due to the retention of chlorophyll in the maternal tissue that surrounds the developing seed. The green pigment filters the light that reaches the seeds. Seed germination increases following a period of dry-storage.
Oxford ragwort seeds germinate in spring and in autumn. When seeds were sown in a 75 mm layer of soil in cylinders in the field and stirred periodically some emerged soon after sowing in autumn but most seedlings emerged in the following year. Just a few odd seedlings emerged in the subsequent 4 years of the study. The main period of emergence was February to September with peaks in April-May and August-September. Flushes of emergence tended to follow cultivations. Seedlings establish best on bare ground or in gaps in the vegetation.
The plant remains green through the winter.
Seeds persist only briefly in soil.
The plumed seeds are wind dispersed. In the UK, Oxford ragwort has spread rapidly via the rail network.
Oxford ragwort is absent from grazed and mown grassland. In arable land normal soil cultivations will control the weed.
Updated September 2007