Epicuticular waxes and vascular plant systematics: integrating micromorphological and chemical data

Plant surfaces are generally not smooth but show considerable variation of microstructures on different scales. One of the most prominent structural elements is epicuticular wax, which exhibits a great micromorphological and chemical diversity, and which is of fundamental functional and ecological importance for the interaction between plants and their environment. The individual morphology of wax crystals depends mainly on their chemical composition. Twenty-three different morphologically defined wax types have been described, several of which are restricted to certain taxa or groups of taxa and, therefore, have systematic significance. Based on high-resolution SEM analysis of at least 13,000 species, representing all major groups of vascular plants, an over-view is given of the systematically most important wax types. Major results are: small tubules built up by the secondary alcohol nonacosan-10-ol (Berberis-type) are characteristic of Ranunculales and allies. Transversely ridged rodlets containing the symmetric ketone plamitone (Aristolochia-type) occur in Magnoliales, Laurales, and Aristolochiales. Epicuticular waxes in monocots reflect two major lineages: (1) Liliales, Asparagales, Burmanniales, and Triuridales with crystals in orientation patterns resembling electromagnetic field lines (Convallaria-type); and (2) Arecales, Pandanales, Velloziales, Typhales, Bromeliales, Zingiberales, Juncales and Poales with longitudinally aggregated rodlets (Strelitzia-type). These and further data are plotted on dahlgrenograms and discussed in light of recent molecular phylogenies.