Fire response may also furnish an explanation for the evolution of this species. The differences in fire regime between dune crests and swales would have created different evolutionary pressures, with plants on crests adapting to frequent hot fires by becoming strongly serotinous, and plants in swales adapting to patchier, cooler fires with weaker serotiny. Speciation would be made possible by the much reduced genetic exchange between crest plants and swale plants, although evidence suggests that there was some introgression at first. Eventually, however, the need for weakly serotinous plants to produce ripe seed by the bushfire season would have brought forward its flowering season until the flowering seasons no longer overlapped; thus a phenological barrier to exchange was erected, allowing the two populations to drift independently of each other.