primary thickening meristem

The primary thickening meristem is a type of meristematic tissue in plants responsible for increasing the girth and thickness of stems and roots, a process known as secondary growth. Unlike apical meristems, which are found at the tips of roots and shoots and contribute to primary growth (lengthening), lateral meristems like the vascular cambium and cork cambium are responsible for secondary growth.12

In woody plants, the vascular cambium produces secondary xylem (wood) and secondary phloem, while the cork cambium produces cork, forming the outer bark. This secondary growth allows plants to increase in diameter, providing greater structural support and enhancing their ability to transport water and nutrients. In some monocots, a primary thickening meristem can produce large amounts of parenchyma, contributing to stem thickness without secondary growth in the typical sense.345