Hybridisation in bladder ketmia weeds ('Hibiscus trionum', Malvaceae)

Hybridisation, particularly in plants, has been recognised as a potentially creative evolutionary process. In weeds, introgressive hybridisation between introduced and native species can result in various forms of hybrids that are more vigorous and potentially more invasive than parental types. This project examines hybridisation between two 'Hibiscus' taxa that are major annual weeds of cultivated and disturbed sites. These taxa are sympatric over part of their range in central NSW and southern QLD. We investigated components of fitness in introduced 'H. trionum' var. 'trionum', native 'H. trionum' var. 'vesicarius', and their reciprocal F1 hybrids under glasshouse conditions. We compared the four cross types and found that seed set was significantly less for the reciprocal crosses compared with the within variety crosses. Seed germination did not differ, although early seedling growth of hybrids has been more vigorous. We will also examine vegetative growth at later stages and sexual reproduction. The results will be discussed in terms of the potential of the hybrids as weeds and genetic erosion of the native taxa.