Since the last century the study of floral symmetry has been characterized by several peaks of special interest. At present, it is a hot topic in two fields, (1) an intrinsic one: molecular genetics of flower development, with the identification of genes that regulate floral symmetry, and (2) an extrinsic one: the significance of symmetry in pollination biology, especially its perception by pollinators. To elucidate evolution of floral symmetry it is important to focus on the diversity of symmetry patterns through the angiosperms. The conventional symmetry pattern designations may encompass very different floral forms that are not necessarily homologous. Thus they are not sufficient for evolutionary considerations: monosymmetry in flowers of basal angiosperms, e.g., is based merely on absence or presence of organs at particular sites, while in asterids it is based on differential development of synorganized floral parts in different floral regions. Asymmetric flowers may simply have an unordered pattern but they may also be highly sophisticated and be based on a high degree of order. Furthermore, the expression of symmetry may greatly change during floral development, such that, e.g., initially more or less polysymmetric flowers may become monosymmetric during development or vice versa. Also the time when the final symmetry pattern arises in development may be quite different from group to group. Although the overall pattern tends to be stable in larger groups, there is often surprising variation even within an individual in earliest development, but with later compensation. There are several larger, successful groups in angiosperms with elaborate monosymmetric flowers (such as Lamiales, Asterales, Fabaceae, Orchidaceae, Zingiberales and Poaceae). Most of these have also developed taxa with asymmetric flowers. Each group has its own idiosyncrasies in floral symmetry. It would be interesting to know to what extent this is also based on a diversity of genetic mechanisms.

Key words: development, diversity, evolution, flowers, symmetry