Abstract
Pollination syndromes evolved under the reciprocal selection of pollinators and plants (coevolution). Here, the two main methods are reviewed which are applied to prove such selection. (i) The indirect method is a cross-lineage approach using phylogenetical trees to understand the phylogeny. Thus, features of single origin can be distinguished from those with multiple origins. Nearly all pollination modes originate in multiple evolutionary ways. (ii) The most frequent pollinators cause the strongest selection because they are responsible for the plant's most successful reproduction. The European sexually deceptive orchid genus Ophrys provides an example of a more direct way to prove selection because the attraction of a pollinator is species specific. Most members of the genus have remarkably variable flowers. The variability of the signals given off by the flowers enables the deceived pollinator males to learn individual flower patterns. They thus avoid already visited Ophrys flowers, interpreting them as females rejecting them. As the males will not return to these individually recognizable flowers, the pollinators´ learning behavior causes cross-pollination and prevents the orchid's self-pollination.