May be dead at maturity. The secondary cell wall of a sclerenchyma cell is often thicker than other cell types in the same plant structure, but it is not always easy to distinguish from tracheary elements (PO:0000290) or sclerified parenchyma cells (PO:0000074). Compare with collenchyma cells (PO:0000075) that are always alive at maturity, have irregularly thickened primary cell walls, and do not have lignified secondary cell walls. Collenchyma cells provides flexibility while sclerenchyma cells provide hardness. Sclerenchyma cells include plant fiber cells (PO:0025407) and sclerid cells (PO:0025418).