GERMINATION BEHAVIOR OF THE RADIATE AND NON-RADIATE MORPHS OF GROUNDSEL, SENECIO-VULGARIS L

Comparisons of the germination behaviour of seeds of the radiate and non-radiate morphs of Senecio vulgaris produced in spring and autumn were made in controlled environments and in the field. Fresh seeds of the non-radiate morph frequently germinated more readily than fresh seeds of the radiate morph during the first flush of germination after sowing. In two field experiments in which germination of freshly produced autumn seeds was tested over an extended period, an initial flush of germination occurred before winter set in, during which more non-radiate than radiate seeds germinated; there then followed a long dormant phase that spanned the winter months before germination resumed in early spring. Over spring more radiate than non-radiate seeds germinated and the net effect was that by mid-spring there was no difference between the cumulative percentage germination of seeds of the two morphs. It is concluded that whereas fresh non-radiate seeds of S. vulgaris tend to show a pattern of germination skewed towards early germination, radiate seeds, produced in autumn, often show a pattern skewed toward late germination. The importance of this difference is briefly discussed in relation to the maintenance of the polymorphism for capitulum type in British populations of S. vulgaris.