The radiate and non-radiate capitulum morph of senecio vulgaris L. within Sussex: the use of GIS in establishing origins

The geographical distribution of the radiate morph of Groundsel (Senecio vulgaris), Senecio vulgaris var. hibernicus was examined in the county of Sussex in southeast England using records from 1980 and 2000. In addition the geographical distribution of Oxford Ragwort (Senecio squalidus) was also investigated for the same area. The spatial distribution of S. squalidus was strongly correlated with the past and present railway network, as is that of . vulgaris var. hibernicus. The number of 2 × 2 km squares containing the radiate morph of S. vulgaris have declined since 1980, though those with S. Squalidus have remained more or less the same. The spatial evidence presented supports the hypothesis that the radiate morph of S. vulgaris occurs because of hydridisation and introgression betweeb the native non-radiate form of S. vulgaris and S. squalidus.