The long and the short of it: long-styled florets are associated with higher outcrossing rate in Senecio vulgaris and result from delayed selfpollen germination

Background: It has been reported that some plants of the self-compatible species Senecio vulgaris produce capitula containing long-styled florets which fail to set seed when left to self-pollinate, although readily set seed when self-pollinated by hand. Aims: To determine if production of long-styled florets is associated with higher outcrossing rate in S. vulgaris, and whether long-styles occur in non-pollinated florets, whereas short-styles are present in self-pollinated florets. Methods: The frequency of long-styled florets was compared in the radiate and non-radiate variants of S. vulgaris, known to exhibit higher and lower outcrossing rates, respectively. In addition, style length was compared in emasculated florets that were either self-pollinated or left non-pollinated. Results: Long-styled florets were more frequent in the higher outcrossing radiate variant. Following emasculation, long styles occurred in non-pollinated florets, while short styles were present in self-pollinated florets. The two variants did not differ in style length within the non-pollinated or within the self-pollinated floret categories. Conclusions: A high frequency of long-styled florets is associated with higher outcrossing rate in S. vulgaris and results from delayed self-pollination and pollen germination on stigmas.