The aim is to provide an understanding of the botanical elements (and their combinations) involved in plant architecture and rules for simulating and modeling plant growth and development (the botanical concepts used in the GreenLab model). The structure of a plant is an intricate organization shaped by genetics, modulated by the environment, and resulted from the interaction between development and growth. The phytomer, comprising the internode and node with leaves, flowers, and buds, is the basic unit of plant structure, produced by the terminal meristem of a leafy axis. The meristems’ ages (chronological, ontogenic, physiological ages) are crucial for understanding plant development. Thermal time, calculated as the sum of temperatures, is used to track the chronological age of meristems, as it provides a stable measure of their functioning. Plant Structures are organized into architectural models based on meristem functions and growth patterns, applicable to all plant types, and can be represented in chronological or topological modes.