Bladder ketmia ('Hibiscus trionum' L.) in Australia - a variable taxa

Accurate identification is important for the management of weed species for a range of different reasons including the selection of effective herbicides, implementing timely management before seed set and for the selection of appropriate biological control agents. Bladder ketmia ('Hibiscus trionum' L.) is extremely variable in Australia with at least three weedy forms occurring. This study assessed variation within and between these forms in a range of field and glasshouse studies. The field studies illustrated a number of differences between narrow and wide leaf forms of bladder ketmia, and determined that two phenotypes of the wide leaf form existed, one with a cream or yellow centred flower and the other with a red centred flower. Glasshouse studies were used to evaluate the biotypic differences between 29 populations of 'H. trionum' taxa collected broadly from within the northern grain zone (Emerald in central Queensland to Narromine in central New South Wales). There was significant variation between 'H. trionum' taxa in many of the 67 growth parameters measured. There was also significant variation in these parameters within different populations of the same taxon. These studies indicate two important areas for further investigation. Firstly, management recommendations, including the timing and choice of herbicides, need to be re-evaluated since important differences exist within this species. Secondly, a taxonomic review of taxa under the name 'H. trionum' is needed to determine if it comprises more than one species.