What are sclereids and what functions do they serve?

Sclereids are a type of sclerenchyma cell characterized by thick, heavily lignified cell walls and a relatively short, irregular shape. Unlike fibers (the other type of sclerenchyma), sclereids are typically isodiametric or branched and occur in various forms including stone cells, astrosclereids, and macrosclereids. These dead cells at maturity provide mechanical support and protection to plant tissues. Sclereids are responsible for the gritty texture in pears, the hardness of seed coats, and the shell of nuts. Their thick walls, containing lignin and sometimes silica, make them extremely resistant to mechanical stress and degradation, protecting delicate tissues and seeds from damage and predation.