Variation within Common Groundsel, Senecio vulgaris L. II. Local differences within cliff populations on Puffin Island

Differences of height between plants from subjectively determined exposed and sheltered sites were examined in two cliff populations of Senecio vulgaris L. from Puffin Island, Anglesey, N. Wales. Under glass the relative dwarf habit of exposed plants from a N. cliff site was retained in their progeny throughout development, but for S. cliff material there was no difference in height between progenies of exposed and sheltered plants at maturity. It was inferred that within the N. cliff site, genetic variability seems to parallel variation in exposure. But in the S. cliff site response to different levels of exposure is mainly facilitated by a wide measure of developmental flexibility for height. It is suggested that the apparent difference of adaptive strategy between the two cliff populations some 500 m apart may be explained in terms of disparate wind speeds in the respective sites. The N. cliffs are particularly exposed to strong winds and under these conditions it is possible that genetic adaptations to the separate micro-environments enhances survival.

The reported predominant self-pollination within S. vulgaris (Trow, 1912; Hull, 1974) is considered in discussion to be of value to an ephemeral as a means of adapting it to the local micro-habitats in a heterogeneous environment, so perpetuating the between plant variability. There are indications that the observed pattern of localised genetic variation on Puffin Island, both between and within populations, has evolved over the last 20 years.