This chapter introduces a detailed mathematical model for simulating plant growth, with a focus on integrating physiological crop models to accurately represent biomass production and distribution. The GreenLab model allows for the analysis of individual plant growth at the phytomer level, reconstructing the plant’s three-dimensional (3D) architecture from a two-dimensional (2D) planar structure formed by meristem function. Based on a source-sink functioning process, organs within the model are assigned specific roles in biomass production and allocation. The model calculates the biomass demand by evaluating the sink strength of organs produced per cohort, considering their physiological and chronological ages. The model uses a recurrence mechanism starting from the seed to track the growth and development of plants over time. The integration of allometric relationships ensures that the organ morphology is consistent with their functional roles. The use of physiological age allows to decompose the plant structure in separated pieces of phytomer axes, known as organic series. Organic series contain the plant growth memory. The organic analysis method infers growth parameters from plant architecture, aiding in data restoration. This mathematical model not only bridges the gap between functional–structural and physiological crop models but also provides a practical approach to crop production and agronomic applications.