Sclerenchyma: Definition, Characteristics, & Types

Sclerenchyma is a type of permanent cell tissue that long, narrow cells with thick walls with few pits. Sclerenchyma is one of the simple tissues among other types of tissues such as parenchyma and collenchyma. Sclerenchyma cells are usually found in stems, leaves of the plants, and in some cases in the roots.

Key Terms: Tissue, Permanent Tissue, Cell, Cell Wall, Plants Firbres, Roots, Plant Cell

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What Is Sclerenchyma? 

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Sclerenchyma is a plant support tissue made up of a variety of hard woody cells. Sclerenchyma tissues are made up of long, narrow cells with thick, lignified cell walls and a few or several pits. Sclerenchyma could be classified as fibers or sclereids based on differences in form, structure, origin, and development. 

Sclerenchyma cells that have grown old are usually dead cells with substantially thickened secondary walls containing lignin. In plants, sclerenchyma is one of three different forms of ground, or fundamental, tissue while the other two are Parenchyma and Collenchyma.

Sclerenchyma cells occur in many different shapes and sizes, but two main types occur are: 

• Fibers: The fibers are thick-walled, elongated, and pointed cells, generally occurring in groups, in various parts of the plant such as stems, leaves, and roots. Seed hairs, leaf fibers, and bast fibers, for example, are essential sources of raw material for textiles and other woven goods.
• Sclereids are dead cells that are spherical, oval, or cylindrical in shape and have very thin cavities (lumen). These are often found in the fruit walls of nuts, the pulp of fruits such as guava, pear, and sapota, legume seed coatings, and tea leaves. Organs are supported mechanically by sclerenchyma.

Sclerenchyma

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Characteristics Of Sclerenchyma

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The characteristics of a sclerenchyma tissue are as follows.

• It's a simple permanent ground tissue that's dead.
• Sclerenchyma serves the same purpose as collenchyma tissue in providing mechanical support and tensile strength to plants.
• Sclerenchyma cells act as a "skeleton" for the plant system, adding stiffness to help it survive varied environmental pressures.
• Sclerenchyma cells persist as living cells during the plant's early development cycle, forming spiral or ring patterns.
• Based on the morphology of sclerenchyma tissue, the three most common forms are fibers, sclereids, and tracheary components.
• The cell wall is divided into two layers: the main cell wall and a thicker secondary cell wall.

Also Read: 

Three Basic Types Of Plant Tissues

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Types Of Sclerenchyma Tissue

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According to the function: Mechanical sclerenchyma and conductive sclerenchyma are the two types of sclerenchyma tissue.

Mechanical Sclerenchyma:-

Mechanical sclerenchyma tissue serves as a supporting tissue in plants, preventing wilting, preserving plant physiology, and providing strength to endure the tearing forces of waves and current. 

Mechanical sclerenchyma is made up of sclereids and fiber cells that provide the plant system with its strength and rigidity. Mechanical sclerenchyma can be classified as follows:

1. Sclereids

Mechanical tissues that exist alone or in clusters are referred to as sclereids. They are present in the vascular tissue of plants, specifically the xylem and phloem. In sclereids, cell wall thickening is not uniform.

There are a few small pits with round apertures in them. Sclereids have a small lumen by nature. The sclereid cells are divided into the following classes based on their shape:

• Macrosclereids
• Osteosclereids
• Astrosclereids
• Brachysclereids
• Trichosclereids
• Filiformsclereids

Six Types of Sclereids

2. Fibre

Fibres are elongated, thick-walled mechanical tissues having a small lumen and tapering ends. The plant's ground and vascular tissues are mostly made up of them. The xylem and phloem tissues have fiber sclerenchyma as a cell partner. 

They appear as strands or cylinders that are autonomous from one another. Based on the shape fiber cells can be categorized into the following groups:

• Xylary Fiber
• Extraxylary Fiber

Conductive Sclerenchyma:-

Conductive Sclerenchyma is made up of a tracheary element, a characteristic of vascular plants that differentiates them from non-vascular plants. Both strength and water conduction are provided by the tracheary elements. 

Tracheary elements occur in vascular plants and include vessel elements and tracheids.

• Vessel Element: They are found in primary and secondary xylem and have perforated end walls (primary and secondary lignified walls). Water conduction is more effective with vessel elements, as water travels vertically from one cell to the next with no obstructions.
• Tracheid: They're the xylem's most frequent cells, appearing spindle-shaped and elongated with tapered ends. They help with water conduction as well as mechanical support. Tracheids are elongated in comparison to vessel parts and have a secondary wall thickening as a frequent feature.

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Things To Remember

• Sclereids support the neighboring tissues and protect the inner cells by forming a concentrating layer towards the periphery.
• Plants benefit from the flexibility provided by fiber tissues. The septate fibers serve as storage cells, storing starch and oil droplets while also protecting the surrounding interior tissues. 
• Water conduction is the sole function of tracheary or vascular elements. The high surface-to-volume ratio of the tracheid protects the plant from air embolisms and water stress.

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