In recent years, the mechanisms of the origin and development of a flower, which is a characteristic structure of angiosperms, became one of the most intensively studied problems in modern evolutionary studies. Two decades ago, the research of two independent scientific groups, led by E. Coen and E. Meyerowitz on Anthirrhinum majus and Arabidopsis thaliana flowers respectively, resulted in a model of the genetic regulation of the successive whorls (sepals, petals, stamens and carpels) development within the flower, called ABC model.

New developments in molecular genetics, explaining over the past decade the changes in floral organ identity and distribution, are presented and discussed. Specific mutations of homeotic genes changing flower phenotype are described as factors leading to the outstanding diversity of floral patterns present in Angiosperms. Special attention is paid to the systems interacting with each other as well as acting independently. Aspects of meristic variation are underlined as important for the development of different floral symmetry in evolutionary lines of Monocots and Eudicots.