meristemen

Meristems are plant tissues composed of actively dividing, undifferentiated cells with the capacity to differentiate into various specialized cell types. They enable growth by producing new cells for developing organs and tissues, supporting both primary growth in length and, in some plants, secondary growth in thickness.

Meristems occur in several forms. Apical meristems are located at the tips of shoots and roots and initiate primary growth. Intercalary meristems, common in many grasses and some monocots, occur at leaf bases or node regions to allow rapid regrowth after damage. Lateral meristems, such as the vascular cambium and cork cambium, generate secondary tissues and contribute to increased girth.

The basic organization includes initial cells and derivatives that divide, enlarge, and differentiate into dermal, ground, or vascular tissues. In shoot apical meristems there is a tunica-corpus arrangement that functions as a regulatory center for stem cell maintenance and patterning of new organs. Root apical meristems sustain elongation and formation of root structures.

Meristem activity is regulated by hormonal signals, particularly auxins and cytokinins, and by gene networks that maintain stem cell pools and control organ initiation, such as WUSCHEL and CLAVATA in the shoot apex.

The term meristem, from Greek and introduced in the 19th century by Karl Nageli, denotes this undifferentiated, growth‑driving tissue. Meristematic tissue is widely used in horticulture and plant biotechnology, including tissue culture for rapid propagation and virus‑free plant production.

Meristems underpin plant form, regeneration after injury, and adaptation to diverse environments.