Eucalypt phytoglyphs: The micronanatomical features of the epidermis in relation to taxonomy

Abstract

The eucalypt leaf contains a store of untapped information of potentially great value taxonomic and evututionary studies. Tie cuticie of certain eucalypts is shown to possess a complex and species-specific ornamentation so distinctive that its features can be regarded as diagnostic. The term "phytoglyph" is coined for the constellation of microanatomical features of the surfaces of leaves, including the microanatomy of the cuticle. Phytoglyphic analysis relates to the combination of three methods, light microscopy of stained cuticles, scanning electron microscopy of leaf surfaces, and light microscopy of thin sections of the cuticular and associated structures. Its use is illustrated by the dissection of the "form species" E. dichromophloia into a number of separate and recognizable entities, some of which were previously accorded the status of species. The plant geographical and other implications of this dissection are dealt with. In particular, E. dichromophloia F. Muell. is to be regarded as a species of very restricted distribution. The microanatomical characters of the cuticle are closely controlled products of the epidermal layers. The fact that specimens which (on other grounds) can be grouped together as a species have identical cuticular microanatomy suggests that the phytoglyph is genetically strongly determined and does not consist of inadvertent, trivial surface features with a high degree of plasticity. This in turn raises the problem of the development of the cuticular microanatomy which cannot be explained on current views of the formation of the cuticle by passive diffusion of precursor substances through the epidermal walls, followed by a hardening process.