XVI International Botanical Congess

Five morphologically distinct species of Ranunculus hybridise extensively in the alpine region of mainland Australia. Hybrids are found in narrow ecotones between the habitats occupied by each species. The species are interfertile, as revealed by artificial crossing, with F1 and F2 interspecific hybrids viable and fully fertile. AFLP and allozyme markers indicate that the species are genetically distinct with narrow clines in morphology corresponding to narrow clines in gene frequency. Interspecific pollen dispersal results in substantial hybrid seed set within parental populations where hybrid adults are absent. It is hypothesised that hybrid zones are stabilized by disruptive selection against hybrids within parental habitats. The performance of parental and hybrid seedlings planted into parental habitats strongly supports this hypothesis.