Types of Stomata

Stomata are classified based on their structure, distribution, and arrangement of guard cells. The details of types of stomata are given below:

Based on the Number and Arrangement of Surrounding Cells

Stomata can be classified into several types based on the number and arrangement of the cells surrounding them, known as subsidiary cells. These classifications are important for understanding plant taxonomy and physiology. The main types are:

Anomocytic Stomata (Irregular-celled type)

• The guard cells are surrounded by a variable number of cells that are indistinguishable from other epidermal cells. There is no specific arrangement or pattern to the surrounding cells.
• The surrounding cells do not have any particular size or shape.
• The arrangement appears random and lacks a structured pattern.
• Examples: This type is commonly found in many dicot families such as Ranunculaceae and Papaveraceae.

Anisocytic Stomata (Unequal-celled type)

• The guard cells are surrounded by three subsidiary cells, where one is distinctly smaller than the other two. This uneven size of surrounding cells is a defining feature.
• Three subsidiary cells surround the guard cells.
• One of the subsidiary cells is significantly smaller than the other two.
• Examples: Commonly seen in families like Solanaceae (e.g., tobacco, potato) and Brassicaceae (e.g., cabbage, mustard).

Paracytic Stomata (Parallel-celled type)

• The guard cells are flanked by two subsidiary cells that are oriented parallel to the long axis of the stomatal pore and the guard cells.
• Two subsidiary cells are positioned alongside the guard cells.
• The subsidiary cells are parallel to the guard cells and the pore.
• Examples: Found in families such as Rubiaceae (e.g., coffee) and Fabaceae (e.g., beans, peas).

Diacytic Stomata (Cross-celled type)

• In this type, the guard cells are surrounded by two subsidiary cells that are oriented perpendicular to the long axis of the stomatal pore.
• Two subsidiary cells flank the guard cells.
• The subsidiary cells are positioned perpendicular to the guard cells and the pore.
• Examples: Seen in families like Caryophyllaceae (e.g., carnations) and Acanthaceae.

Actinocytic Stomata (Radiate-celled type)

• The guard cells are surrounded by a circle of radiating subsidiary cells, resembling the spokes of a wheel.
• Multiple subsidiary cells encircle the guard cells.
• The arrangement is radial, giving a star-like appearance.
• Examples: Found in some monocot families such as certain grasses.

Based on the Evolutionary Development

Stomata can also be classified based on their evolutionary development, defining the different origins and mechanisms by which they form during plant evolution. The main types are:

Haplocheilic Stomata

• These stomata develop from a single initial cell that divides to form both the guard cells and the surrounding subsidiary cells. This type of stomata development is considered more primitive.
• The entire stomatal complex, including guard cells and subsidiary cells, arises from a single progenitor cell.
• The developmental process is relatively simple and direct.
• Examples: Haplocheilic stomata are commonly found in ferns and some gymnosperms.

Syndetocheilic Stomata

• In this type, the guard cells and subsidiary cells develop from multiple initial cells. The development process is more complex compared to haplocheilic stomata.
• The guard cells and subsidiary cells originate from different initial cells.
• This type of development allows for a more complex arrangement of cells.
• Examples: Syndetocheilic stomata are typical in most angiosperms (flowering plants), which represent a more advanced stage of plant evolution.

Based on the Developmental Origin

Stomata can also be classified based on their developmental origin, which refers to how the guard cells and subsidiary cells are formed during the growth of the plant. The two main types based on developmental origin are mesogenous and perigenous stomata.

Mesogenous Stomata

• In mesogenous stomata, both the guard cells and the subsidiary cells originate from the same initial epidermal cell. This initial cell undergoes a series of divisions to form the complete stomatal complex.
• The initial cell, also known as the meristemoid, divides to produce guard cells directly as well as subsidiary cells.
• The development is a coordinated process where the same progenitor cell gives rise to all the components of the stomatal apparatus.
• Examples: Common in monocot families such as Poaceae (grasses) and Liliaceae (lilies).

Perigenous Stomata

• In perigenous stomata, the guard cells and the subsidiary cells originate from different initial cells. This means the subsidiary cells are derived from neighboring epidermal cells, not the same initial cell that forms the guard cells.
• The guard cells arise from one initial cell, while the subsidiary cells come from adjacent cells that do not share the same lineage as the guard cells.
• This type of development can result in a more varied and less coordinated arrangement of the stomatal complex.
• Examples: Common in dicot families such as Asteraceae (daisies) and Fabaceae (legumes).

Stomata are small pores on leaf and stem surfaces essential for gas exchange and transpiration in plants. Each stoma is controlled by two guard cells that regulate its opening and closing. The distribution and structure of stomata vary, with dicots having more on the lower leaf surface and monocots having them evenly distributed.

Stomata can be classified based on the number and arrangement of surrounding cells, evolutionary development, and developmental origin. In this article, we will study the stomata and its types and functions in detail.