The leaf waxes of the genus Eucalyptus L'Héritier

Abstract

A survey of 315 species of the genus Eucalyptus demonstrated that the patterns of leaf wax structure as revealed by means of electron microscopy can in some instances aid the classification of this taxonomically complex genus. Within Eucalyptus there are three main wax types: plates, tubes, and a mixed wax of both plates and tubes. The degree of ornamentation of the margins of the plates can frequently be correlated with taxonomic groupings or suggested evolutionary trends based on other lines of evidence. Similarly tube waxes, depending on their branching pattern and arrangement on the leaf surface, also proved useful as indicators of natural groupings of species. A number of taxa known to be misfits on various morphological characters within the most widely used classification of the genus (Blakely's "Key to the Eucalypts") are also shown to be misfits on the basis of wax characters. Already recognized affinities of large groups of species within the genus are supported by evidence from wax morphology. A study of the chemistry of eucalypt waxes by means of infrared and ultraviolet absorption spectroscopy confirms many of the results of the taxonomic study based on wax morphology.