This chapter presents the case of herbaceous plants whose growth and development show great architectural variability. The GreenLab model is adapted to account for these differences, with herbaceous plants forming new phytomers much faster than woody plants. The chapter also discusses the phenological stages of rosette-forming herbaceous plants, which have a distinct vegetative phase followed by a reproductive phase. The expansion of phytomers does not immediately follow their creation; instead, branches remain preformed until flowering is triggered. In contrast to woody plants, the growth and development of organ cohorts in herbaceous plants are not synchronized. The expansion of preformed organs is delayed and depends on their creation time, their type, and their position within the plant’s topological structure. The organic series need to be adapted using simple or compound organic series. This complexity necessitates calculations to be performed in list mode rather than matrix mode, as previously described. Despite these challenges, the computational cost remains manageable due to the reduced development cycle of herbaceous plants compared to trees.