Information regarding polymorphism of floral structure is important for understanding the genetic and evolutionary mechanisms of flower development. Penin and Logacheva conduct a wide survey of the variations in number and position of floral organs in Arabidopsis thaliana, including both wild type and mutants with altered floral structure. They find that the organs located in the medial zone of the flower, petals and stamens, are the most unstable. The position of petals is correlated with that of sepals, and the position of stamens with that of carpels. This suggests that the positions of organs in the basal and apical parts of the flower are determined before those in the intermediate zone.