The utility of isozymes in the systematics of some Australian tree groups

Abstract

The utility of isozyme analysis in elucidating the relationship between Australian tree taxa is reviewed. Although little exploited to date, isozyme analysis is shown to be a rapid and relatively powerful method of examining relationships, if used at an appropriate taxonomic level. For Eucalyptus and Acacia, isozymes appear to be the most informative at the lower taxonomic levels. In Eucalyptus delegatensis and Casuarina cunninghamiana, isozyme data strongly support subspecies erected on the basis of morphological characteristics. In Acacia holoserocea, isozyme data predicted the existence of two subspecies, which prediction as later supported by morphological characters. An isozyme study of the phylogenetic relationships within the 'green ash' group of eucalypts yielded a phylogenetic hypothesi comparable to one derived from morphological characters, but also highlighted areas of discrepancy requiring further research. At the generic level, isozyme data for the Australian species of Litsea and Neolitsea successfully separated the two genera and allowed phylogenetic relationships within genera to be hypothesised. For the larger tree genera such as the Eucalyptus and Acacia, however, the utility of isozymes at the higher taxonomic levels is likely to be low, because of the difficulty in establishing homologies between taxa, or insufficient phylogenetic information when taxa being compared have few alleles in common.