Sclerenkym

Sclerenkym, or sclerenchyma, is a plant tissue specialized for mechanical support and protection. It is composed of sclerenchyma cells that are typically dead at maturity, with thick, lignified secondary cell walls that provide rigidity and strength. The cells usually have little to no cytoplasm when fully developed.

There are two main sclerenchyma cell types. Fibers are elongated, slender cells that occur in long strands or bundles in stems, roots, and other organs, contributing tensile strength. Sclereids are shorter and more varied in shape; they include brachysclereids (stone cells) found in seed coats, nutshells, and gritty textures in some fruits. The diversity of sclereids helps to protect seeds and other tissues.

Sclerenchyma is widely distributed in vascular plants. It is common around vascular bundles, within the periphery of stems, in roots, and in various protective structures such as seed coats and nutshells. In many fruits, sclereids contribute to a gritty or woody texture, as in pears or coconuts.

The development of sclerenchyma involves thickening of the cell wall through lignification, often at the expense of cytoplasm. Mature sclerenchyma cells are typically dead, which prevents further growth but allows the tissue to retain its shape and strength under mechanical stress.

Compared with other plant strengthening tissues, sclerenchyma is rigid and inelastic, providing long-term support. Parenchyma cells are living and more metabolically active, while collenchyma cells have thickened but living primary walls and offer flexible support.