Abstract: We present a modelling method and graphical user interface for the creation of natural branching structures such as plants. Structural and geometric information is encapsulated in objects that are combined to form a description of the model. The description is represented graphically as an icon tree and can be edited interactively. Global and partial constraint techniques are integrated on the basis of tropisms and allow the modelling of specific shapes. We show examples to illustrate the design process and evaluate the user interface.