Reduction in pollen fertility in artificially crossed interspecific hybrid strains of Asimitellaria. Boxes and error bars represent the range distribution for individual strains, with thick horizontal bars representing the median. (a) Crosses within clade A. (b) Crosses within clade B. (c) Crosses within clade C. The strain ID numbers are as in Table 1. Note that the strain IDs 1–9 are the wild-collected individuals used as controls.