Wilhelm Barthlott

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 significance. Waxes are an essential structural element of the surface and of fundamental functional and ecological importance for the interaction between plants and their environment. An extensive literature has been published since the introduction of scanning electron microscopy (SEM). Hitherto, the area has lacked a complete classification and terminology necessary as a standard for comparative descriptions. A refined classification and terminology of epicuticular waxes is therefore proposed based on high-resolution SEM analysis of at least 13 000 species, representing all major groups of seed plants. In total 23 wax types are classified. Thin wax films appear to be ubiquitous, while thicker layers or crusts are rare. The most prominent structures are local wax projections, which most probably result from self-assembly of wax molecules. These projections are supposed to be mainly of a crystalline nature and are termed crystalloids here. Among these, platelets and tubules are the most prominent types, while platelets arranged in parallel rows and stomatal wax chimneys are the most striking orientation and aggregation patterns. In addition, a comprehensive overview on the correlation between wax ultrastructure and chemical composition is given.

A global assessment of endemism and species richness across island and mainland regions

Endemism and species richness are highly relevant to the global prioritization of conservation efforts in which oceanic islands have remained relatively neglected. When compared to mainland areas, oceanic islands in general are known for their high percentage of endemic species but only moderate levels of species richness, prompting the question of their relative conservation value. Here we quantify geographic patterns of endemism-scaled richness (“endemism richness”) of vascular plants across 90 terrestrial biogeographic regions, including islands, worldwide and evaluate their congruence with terrestrial vertebrates. Endemism richness of plants and vertebrates is strongly related, and values on islands exceed those of mainland regions by a factor of 9.5 and 8.1 for plants and vertebrates, respectively. Comparisons of different measures of past and future human impact and land cover change further reveal marked differences between mainland and island regions. While island and mainland regions suffered equally from past habitat loss, we find the human impact index, a measure of current threat, to be significantly higher on islands. Projected land-cover changes for the year 2100 indicate that land-use-driven changes on islands might strongly increase in the future. Given their conservation risks, smaller land areas, and high levels of endemism richness, islands may offer particularly high returns for species conservation efforts and therefore warrant a high priority in global biodiversity conservation in this century.

Superhydrophobic and superhydrophilic plant surfaces: an inspiration for biomimetic materials

The diversity of plant surface structures, evolved over 460 million years, has led to a large variety of highly adapted functional structures. The plant cuticle provides structural and chemical modifications for surface wetting, ranging from superhydrophilic to superhydrophobic. In this paper, the structural basics of superhydrophobic and superhydrophilic plant surfaces and their biological functions are introduced. Wetting in plants is influenced by the sculptures of the cells and by the fine structure of the surfaces, such as folding of the cuticle, or by epicuticular waxes. Hierarchical structures in plant surfaces are shown and further types of plant surface structuring leading to superhydrophobicity and superhydrophilicity are presented. The existing and potential uses of superhydrophobic and superhydrophilic surfaces for self-cleaning, drag reduction during moving in water, capillary liquid transport and other biomimetic materials are shown.

Diversity of structure, morphology and wetting of plant surfaces

This review paper presents the diversity of plant surface structures from a single cell to multi-cellular surface sculptures. There is still no comprehensive book which provides an overview of the diversity of plant surface structures. This article presents a guide for the description of cellular and sub-cellular plant surface structures, which include hairs, wax crystals and surface folding. Biological surfaces are multifunctional boundary layers to their environment. Functionally optimized surfaces are one of the key innovations in the more than 400 million years of evolution of land plants. In the plant surface, micro- and nanostructures play a special role, and a large diversity of surface structures exists at different size levels. Well known functional aspects of plant surface structures are the reduction of particle adhesion, the sliding structures of carnivorous plants for insect catching, and the self-cleaning properties of the superhydrophobic Lotus (Nelumbo nucifera) leaves. Their structures and functions might be useful models for the development of functional materials. The surface properties of plants are based on physico-chemical principles and can be transferred to technical “biomimetic” materials, as successfully done for the self-cleaning properties of the Lotus leaves. This article is designed as an introduction for biologists and non biologists and should stimulate the reader to initiate or intensify the study of biological surfaces.

Fabrication of artificial Lotus leaves and significance of hierarchical structure for superhydrophobicity and low adhesion

The superhydrophobic and self-cleaning leaves of Lotus (Nelumbo nucifera, Gaertn.) have been used as a model for the development of artificial biomimetic surfaces. The hierarchical structure of the Lotus leaf has been recreated to characterize the influence of hierarchical roughness on superhydrophobicity and adhesion. Hierarchical structures were fabricated by a fast and precise molding of the Lotus leaf microstructure, and self-assembly of the natural Lotus wax deposited by thermal evaporation to create the wax tubules nanostructures. Tubule formation was initiated by exposure of the specimens to a solvent vapor phase at a selected temperature. In order to study the influence of structures at different scale sizes on superhydrophobicity, a flat surface, microstructured Lotus leaf replica and a micropatterned Si replica, and a nanostructure were fabricated. Static contact angle, contact angle hysteresis, tilt angle and adhesive forces were measured. The data show that microstructures and nanostructures lead to superhydrophobicity, whereas hierarchical structures further improve this property and show low contact angle hysteresis, superior to that of the natural Lotus leaves.

Noncoding plastid trnT‐trnF sequences reveal a well resolved phylogeny of basal angiosperms

Recent contributions from DNA sequences have revolutionized our concept of systematic relationships in angiosperms. However, parts of the angiosperm tree remain unclear. Previous studies have been based on coding or rDNA regions of relatively conserved genes. A phylogeny for basal angiosperms based on noncoding, fast‐evolving sequences of the chloroplast genome region trnT‐trnF is presented. The recognition of simple direct repeats allowed a robust alignment. Mutational hot spots appear to be confined to certain sectors, as in two stem‐loop regions of the trnL intron secondary structure. Our highly resolved and well‐supported phylogeny depicts the New Caledonian Amborella as the sister to all other angiosperms, followed by Nymphaeaceae and an Austrobaileya–Illicium–Schisandra clade. Ceratophyllum is substantiated as a close relative of monocots, as is a monophyletic eumagnoliid clade consisting of Piperales plus Winterales sister to Laurales plus Magnoliales. Possible reasons for the striking congruence between the trnT‐trnF based phylogeny and phylogenies generated from combined multi‐gene, multi‐genome data are discussed.

The Salvinia Paradox: Superhydrophobic Surfaces with Hydrophilic Pins for Air Retention Under Water

[*] Prof. W. Barthlott, S. Wiersch, Dr. H. F. Bohn Nees-Institut für Biodiversität der Pflanzen Rheinische Friedrich-Wilhelms-Universität Meckenheimer Allee 170, 53115 Bonn (Germany) E-mail: barthlott@uni-bonn.de Prof. Th. Schimmel, Dr. M. Barczewski, Dr. S. Walheim, A. Weis, A. Kaltenmaier Institute of Applied Physics and Center for Functional Nanostructures (CFN) University of Karlsruhe Karlsruhe Institute of Technology (KIT) 76131 Karlsruhe (Germany) Institute of Nanotechnology and Center for Functional Nanostructures (CFN) Forschungszentrum Karlsruhe Karlsruhe Institute of Technology (KIT) 76021 Karlsruhe (Germany) E-mail: thomas.schimmel@physik.uni-karlsruhe.de Prof. K. Koch Biologie und Nanobiotechnologie Hochschule Rhein-Waal Landwehr 4, 47533 Kleve (Germany)

How plants shape the ant community in the Amazonian rainforest canopy: the key role of extrafloral nectaries and homopteran honeydew

Abstract. Ant-plant interactions in the canopy of a lowland Amazonian rainforest of the upper Orinoco, Venezuela, were studied using a modified commercial crane on rails (Surumoni project). Our observations show a strong correlation between plant sap exudates and both abundance of ants and co-occurrence of ant species in tree canopies. Two types of plant sap sources were compared: extrafloral nectaries (EFNs) and honeydew secretions by homopterans. EFNs were a frequent food source for ants on epiphytes (Philodendron spp., Araceae) and lianas (Dioclea, Fabaceae), but rare on canopy trees in the study area, whereas the majority of trees were host to aggregations of homopterans tended by honeydew-seeking ants (on 62% of the trees examined). These aggregations rarely occurred on epiphytes. Baited ant traps were installed on plants with EFNs and in the crowns of trees from three common genera, including trees with and without ant-tended homopterans: Goupia glabra (Celastraceae), Vochysia spp. (Vochysiaceae), and Xylopia spp. (Annonaceae). The number of ant workers per trap was significantly higher on plants offering one of the two plant sap sources than on trees without such resources. Extrafloral nectaries were used by a much broader spectrum of ant species and genera than honeydew, and co-occurrence of ant species (in traps) was significantly higher on plants bearing EFNs than on trees. Homopteran honeydew (Coccidae and Membracidae), on the other hand, was mostly monopolised by a single ant colony per tree. Homopteran-tending ants were generally among the most dominant ants in the canopy. The most prominent genera were Azteca, Dolichoderus (both Dolichoderinae), Cephalotes, Pheidole, Crematogaster (all Myrmicinae), and Ectatomma (Ponerinae). Potential preferences were recorded between ant and homopteran species, and also between ant-homopteran associations and tree genera. We hypothesize that the high availability of homopteran honeydew provides a key resource for ant mosaics, where dominant ant colonies and species maintain mutually exclusive territories on trees. In turn, we propose that for nourishment of numerous ants of lower competitive capacity, Philodendron and other sources of EFNs might be particularly important.

Superhydrophobicity in perfection: the outstanding properties of the lotus leaf

Summary Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves.

Diversity and abundance of vascular epiphytes: a comparison of secondary vegetation and primary montane rain forest in the Venezuelan Andes

Species diversity of vascular epiphyte plant communities was studied in La Carbonera, a montane rain forest dominated by Podocarpaceae in the Venezuelan Andes. We compared the epiphyte communities of the primary, disturbed, and secondary forest areas of La Carbonera in order to augment the scarce knowledge on the effects of anthropogenic disturbance on these important elements of tropical vegetation. Diversity of vascular epiphytes (191 species in the whole forest area) was low in the disturbed and secondary areas (81 spp.) compared to adjacent primary forest (178 spp.). Four types of disturbed forest and secondary vegetation supported different numbers of epiphyte species, showing a decline with increasing degrees of disturbance (65 spp. along a road transect, 42 spp. on relict trees in disturbed forest, 13 spp. in a tree plantation and 7 spp. in a former clearing, both secondary vegetation units). Epiphytic species composition in primary and disturbed or secondary forest areas differed markedly: disturbed habitats harboured fewer fern and orchid species but more bromeliad species than the primary forest. Probably the families occurring only in primary forest sites of our study may be useful as bioindicators to determine the degree of disturbance in other habitats of mountain rain forests as well. Epiphyte abundance was also lower in disturbed habitats: a remnant emergent tree supported only about half as many epiphyte individuals as a member of the same species of similar size in the primary forest. The decrease in species numbers and abundance as well as the differences in species composition are mainly due to the less diverse phorophyte structure and less differentiated microclimate in the disturbed and secondary vegetation compared to the primary forest.