XVI International Botanical Congess

Sexually reproducing hybrid species can originate at both homoploid and polyploid levels. The hypothesis that such species might originate and establish in sympatry with their parents is difficult to accept if postzygotic sterility barriers alone form the basis of reproductive isolation. This is because the hybrid will initially be rare and consequently most of its offspring will be the sterile products of crosses with neighboring parent types. This minority type disadvantage can be prevented if hybrid material is dispersed to locations ecologically and/or geographically isolated from the parents. Recent studies of speciation in British Senecio have identified a homoploid and a polyploid hybrid species of very recent origin. These studies have shown how these two species originated, and provide information on the importance of ecological and geographical isolation during establishment.