CHARACTERIZATION AND DISTRIBUTION OF WATER-REPELLENT, SELF-CLEANING PLANT-SURFACES

During the last 20 years, a wealth of data dealing with scanning elect ron microscopy of plant surfaces has been published. The ultrastructur e of epidermal surfaces has been investigated with respect to taxonomi c, as well as functional aspects. Within the latter, water-repellency has received much attention and has been well documented. Water-repell ency is based on surface roughness caused by different microstructures (trichomes, cuticular folds and wax crystals), together with the hydr ophobic properties of the epicuticular wax. In addition, contaminating particles are carried away by water droplets, resulting in a cleaned surface (Lotus-effect). Therefore, rough, waxy leaves are not only wat er-repellent but anti-adhesive with respect to particulate contaminati on. Based on 200 water-repellent plant species, the present paper surv eys micromorphological characteristics of anti-adhesive plant surfaces . Leaves that are permanently water-repellent can be differentiated by distictively convex to papillose epidermal cells and a very dense lay er of epicuticular waxes. Leaves that are water-repellent for only a l imited period of time have only slightly convex epidermal cells and of ten have a less dense wax layer. Finally, an overview is given on the occurrence of water-repellency among different life forms and within d ifferent habitats. Water-repellency is concentrated in herbaceous spec ies, while it is rare in trees. Among different habitats, subtropical regions, wetlands and disturbed areas appear to have more species with water-repellent leaves. The importance of roughness and water-repelle ncy, respectively, as the basis of an anti-adhesive, self-cleaning sur face, in comparison to other functions of microstructures, is discusse d. (C) 1997 Annals of Botany Company.