Abstract
Hand pollination under New Zealand field conditions of capitula from each of six populations of Hieracium pilosella (maternal parent) with the closely related but morphologically distinct H. aurantiacum produced F 1 hybrids in every case. The frequency of F 1 hybrid offspring among the populations ranged from 0.2 to 21.6%. Involucral bract characteristics, leaf shape, and petal colour were the most useful characters for identifying hybrid progeny. Most F 1 hybrids were able to set seed by apomixis, but a sexual individual was also recovered. The discovery that both tetraploid and pentaploid H. pilosella can reproduce sexually, following artificial pollination under field conditions, in New Zealand has implications for the bio‐control of this species. Sexually reproducing plants are more likely to evolve resistance to host‐specific bio‐control agents than are apomicts. These results are part of a larger, ongoing research programme investigating the role of the environment in the expression of apomixis.