meristemas

Meristem refers to regions in plants consisting of undifferentiated, actively dividing cells that drive growth and the formation of new organs. Meristematic cells are typically small, with dense cytoplasm and large nuclei, and retain the capacity to differentiate into various specialized tissues. Meristems are classified by position and function into apical, lateral, and intercalary types.

Apical meristems are located at the tips of shoots and roots and drive primary growth, enabling elongation and the generation of new organs such as leaves, stems, and roots. Lateral meristems, including the vascular cambium and cork cambium, contribute to secondary growth, thickening stems and roots in many woody plants. Intercalary meristems occur in some monocots, such as grasses, at bases of leaves or between mature tissues, supporting rapid regrowth after grazing or injury.

During early development, primary meristems arise from the embryo and generate the plant’s fundamental tissues: protoderm forms the epidermis, ground meristem forms cortex and pith, and procambium forms the primary vascular system. The shoot apical meristem contains zones with distinct roles, including a central zone of stem-cell maintenance and peripheral and rib meristems that give rise to leaf primordia and internal tissues, respectively.

Growth and differentiation are regulated by plant hormones, notably auxins and cytokinins, which influence the balance between stem-cell maintenance and organ formation. Meristems are essential for continuous plant growth, regeneration after injury, and the development of form and function in crops, trees, and ornamental species.