This special issue of Botanische Jahrbücher is devoted to flower syndromes and their evolution, which present exciting problems. Floral syndromes characterize flowers ecologically according to their pollination agents. Often in coevolution with pollinators, pollination syndromes evolved to a large extent independently of each other. They often consist of many functionally correlated characters. The change of one or two features may result in the attraction of new flower visitors. A symposium entitled "The evolution of flower syndromes", which was held at the XVII. International Botanical Congress in Vienna on July 20, 2005, brought together active researchers in floral biology - botanists and zoologists - from several countries with the objective of new insights in the evolution of flower pollination at different levels. All contributions of this symposium are included in this volume.

What exactly is a syndrome? This question is discussed by Stefan Vogel (U. of Vienna, Austria). Klaus Lunau (U. Düsseldorf, Germany) reports on the importance of real and mimic stamens in zoophilous plants attracting flower visitors. Andrew A. Beattie (Macquarie University, Australia) reviews the evidence for the scarcity of ant pollination, and indicates the evolution of two very different pollination systems. The occurrence of wind pollination characters evolved in Richea species (Ericaceae) is described by Philip G. Ladd (Murdoch University, Australia). Isabel Cristina Machado and co-workers (Federal University of Pernambuco, Brasilia) report on bat pollination in Cleome spinosa having trimonoecious, andromonoecious and pistillate individuals. A synopsis of different modes of secondary pollen presentation in Astrales and the connection of the mechanisms in a presumed phylogenetic relationship are presented by Peter Leins and Claudia Erbar (University of Heidelberg, Germany). Corinna U. Koch and Otto von Helversen (University of Erlangen, Germany) show special cases of secondary pollen presentation in Cuban bat pollinated Lobelia species.