Variation within Common Groundsel, Senecio vulgaris L. I. Genetic response to spatial variations of the environment

Variation within and between four populations of the highly plastic and ephemeral plant Senecio vulgaris L. has been evaluated for several quantitative characters in three environments and at four stages of development. The populations were from soils of high and low nutrient levels and in habitats of different degrees of exposure. There are significant differences between the means and phenotypic variances of populations for most characters but the degree of difference tends to change both in level and direction between environments and throughout development. However, there are some consistent differences and these seem closely related to the differences between habitats. Of special interest was the variation within populations where it emerged that samples of the populations from sites that were highly heterogeneous for exposure showed much more heritable variation for height and several other characters which might influence the expression of stature than samples from apparently homogeneous sites. It is suggested that though S. vulgaris is capable of showing a wide measure of phenotypic plasticity which could be of adaptive significance in the field, many differences between and within populations may in part be attributed to gene differences that are likely to have resulted from the action of natural selection.