CLASSIFICATION AND TERMINOLOGY OF PLANT EPICUTICULAR WAXES

Plant cuticles are covered by waxes with considerable ultrastructural and chemical diversity. Many of them are of great systematic significa nce. Waxes are an essential structural element of the surface and of f undamental functional and ecological importance for the interaction be tween plants and their environment. An extensive literature has been p ublished since the introduction of scanning electron microscopy (SEM). Hitherto, the area has lacked a complete classification and terminolo gy necessary as a standard for comparative descriptions. A refined cla ssification and terminology of epicuticular waxes is therefore propose d based on high-resolution SEM analysis of at least 13 000 species, re presenting all major groups of seed plants. In total 23 wax types are classified. Thin wax films appear to be ubiquitous, while thicker laye rs or crusts are rare. The most prominent structures are local wax pro jections, which most probably result from self-assembly of wax molecul es. These projections are supposed to be mainly of a crystalline natur e and are termed crystalloids here. Among these, platelets and tubules are the most prominent types, while platelets arranged in parallel ro ws and stomatal wax chimneys are the most striking orientation and agg regation patterns. In addition, a comprehensive overview on the correl ation between wax ultrastructure and chemical composition is given. (C ) 1998 The Linnean Society of London.