Background and Aims : AMAPsim is a tool that implements a structural plant growth model based on a botanical theory and that simulates plant morphogenesis and produces accurate complex and detailed plant architectures. This software is the result of more than a decade of development and research devoted to plant architecture. New advances in the software development allow external functions to be plugged in order to open the simulator to functional processes. Methods : The simulation of plant topology is based on the growth of a set of virtual buds, whose activity is modelled using stochastic processes. The geometry of resulting axes is modelled by simple descriptive functions. The potential growth of each bud is represented through a numerical value called physiological age, which controls every model parameters value. The set of possible values of physiological ages is called the reference axis. In order to mimic morphological and architectural metamorphosis, the value of the physiological age of buds is evolving along this reference axis according to an oriented finite state automaton whose occupation and transition law follows a semi-Markovian function. Key Results : Simulations have been performed on tomato plants in order to show how the AMAPsim simulator can interface external modules, e.g. GreenLab growth model and a radiosity model. Conclusion : The algorithmic ability that is provided by AMAPsim, e.g. the reference axis, allows such unified control of plant development parameter values, depending on biological process target: how to influence the local pertinent process, i.e. the pertinent parameter(s), keeping the rest unchanged. This opening to external functions also offers a large field of applications, hence allowing feedback between plant growth and the physical environment to be performed.