Distribution and Types of Stomata

A. Depending upon the distribution and arrangement of stomata in the leaves five categories of stomatal distribution have been recognized in plants.

1. Apple or mulberry (hypostomatic) type: Stomata are found distributed only on the lower surface of leaves, e.g., apple, peach, mulberry, walnut, etc.

2. Potato type: Stomata are found distributed more on the lower surface and less on its upper surface, e.g., potato, cabbage, bean, tomato, pea, etc.

3. Oat (amphistomatic) type: Stomata are found distributed equally upon the two surfaces, e.g. maize, oats, grasses, etc.

4. Water lily (epistomatic) type: Stomata are found distributed only on the upper surface of leaf, e.g., water lily, Nymphaea and many aquatic plants.

5. Potamogeton (astomatic) type: Stomata are altogether absent or if present they are vestigeal. e.g., Potamogeton and submerged aquatics.

B. Types of Stomata based on Movement

Loftfield (1856) classified three main groups of stomata in accordance with their daily movement:

1. Alfalfa Type: The stomata remain open throughout the day and closed all night, eg., peas, bean, mustard etc.

2. Potato Type: The stomata will open throughout the day and night except for few hours in the evening, eg., Allium, cabbage, pumpkin, etc.

3. Barley Type: The stomata open only for a few hours in a day, eg., Barley and other cereals.

C. Types of Stomata based on Behavior

Considering the behavior of the stomatal movements, five categories have been recognized:

1. Photo-active movements: Light directly or indirectly controls stomatal movements. Such stomata remain open during day time and closed in nights (dark).

2. Skoto-active movements: Stomata remain closed during day time and open during night. Such cases are found in succulent plants and other CAM Plants.

3. Hydro-active movements: In some cases, stomata open due to excessive loss of water from the epidermal cells and close due to turgid conditions of epidermal cells. This is usually found during mid-day.

4. Autonomous movements: In certain cases, stomata open and close at a rate of 10-15 minutes showing diurnal or rhythmic pulsation.

5. Passive and Active movements: Opening of stomata is considered as active process and
closing is the passive process and this is caused by the turgor changes in the guard cells.