Aspects of Hybridization between the Closely Related Senecio vulgaris L. and Senecio vernalis Waldst. & Kit.

Abstract

The results from an investigation of hybridization between closely related Senecio vulgaris (2n = 40) and S. vernalis (2n = 20) are reported. In the two mixed populations examined the frequency of the triploid (2n=30) S. × helwingii was found to be 1.1 and 1.5% respectively. The spatial distribution of hybrid frequency at least in one of the populations examined seems to be roughly correlated with abundance of parent taxa. Hybridization between the two species under experimental conditions is easy. In nature the predominant self-fertilization of S. vulgaris and the rarity of interspecific pollinator flights as observed in a garden trial might be the major factors limiting hybrid formation. Experimental hybridization between F1 hybrids, their backcross to both parent species and self-pollination of the F1 hybrid did not result in hybrid progeny. However, plants could be raised from spontaneously formed achenes on the F1. These were either tetraploid (2n=40) or +/- hexaploid (2n=57-61). It seems likely that these were formed by pollination of the F1 hybrid with pollen from S. vulgaris in the case of the tetraploid and by polyploidization of the F1 hybrid in the hexaploids. In both these pollen and seed fertility recovered remarkably in comparison to the Fl. These processes involving S. vulgaris and S. vernalis are compared to those known from S. vulgaris and S. squalidus in the British Isles.