– Origin
– Sclereids form through belated sclerosis of parenchyma cells or from early individualized sclereid primordia
– Thickening of cell wall increases rigidity during sclerification
– In phloem, cells may sclerify when tissue stops conduction
– Sclereids develop from cambial and procambial cells in vascular tissue
– Stem Sclereids
– Column of sclereids in vascular region of Hoya carnosa stem
– Groups of sclereids in pith of Hoya and Podocarpus stems
– Thick-walled sclereids with numerous pits, resembling parenchyma cells
– Brachysclereids or stone cells are an example of these sclereids
– Leaf Sclereids
– Leaves contain various types of sclereids
– Two distinct sclereid structures in mesophyll: diffuse and terminal patterns
– Examples include branched sclereids of Trochodendron and columnar sclereids of Hakea
– Olive leaves have fiberlike sclereids that increase in size significantly during sclerification
– Fruit Sclereids
– Sclereids in fruits vary in form and function
– Pears have concentric clusters of sclereids with bordered pits
– Apples have elongated sclereids forming endocarp around seeds
– Quince fruit also contains sclereids with bordered pits during thickening
– Seed Sclereids
– Seed coat hardening occurs through sclerification
– Leguminous seeds show thickening of secondary cell walls
– Larger sclereids in pea, bean, and soybean seeds
– Protodermal origin of larger macrosclereids in seed coats
Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants. The presence of numerous sclereids form the cores of apples and produce the gritty texture of guavas.
Although sclereids are variable in shape, the cells are generally isodiametric, prosenchymatic, forked, or elaborately branched. They can be grouped into bundles, can form complete tubes located at the periphery, or can occur as single cells or small groups of cells within parenchyma tissues. An isolated sclereid cell is known as an idioblast. Sclereids are typically found in the epidermis, ground tissue, and vascular tissue.
The term "sclereid" was introduced by Alexander Tschirch in 1885.