How a group of cells develops into a tissue or an organ with a well-defined shape is a long-standing puzzle in developmental biology. Kuchen et al. have used a combination of tracking clones of cells and experimental manipulation in Arabidopsis thaliana leaves, along with computer modelling, to produce a model that accounts for observed growth dynamics and shape changes. In the model, growth orientation is specified by tissue polarity, and this polarity deforms during growth. The model also correctly predicts patterns of clones in growing Antirrhinum majus leaves.