The phloem is the vascular tissue that carries out the function of translocation (i.e. the process of transporting photosynthate materials from the photosynthetic plant organs to various parts of the plant). The phloem is comprised of the following major components: (1) sieve elements, (2) companion cell, (3) phloem sclerenchyma, and (4) phloem parenchyma.
The phloem sclerenchyma is comprised of sclerenchyma cells that are rather associated with providing mechanical support than conducting materials. It includes the phloem fibers and the sclereids. The phloem fibers are one of the supportive cells of the phloem tissue; the others are sclereids. Both the phloem fibers and the sclerieds are specialized forms of sclerenchyma cells that provide mechanical support due to the secondary cell wall that forms in between the primary cell wall and the plasma membrane. Both the phloem fibers and the sclereids have secondary wall that is thickened with lignin. They are dead cells as they lose their protoplast at maturity. The phloem fiber is narrow and elongated whereas the sclereids are irregularly shaped. Unlike sclereids, the phloem fiber does not reduce flexibility.