Placentation in Plants

Ovules are typically attached to the walls of the ovary, often on one or more cushion-like structures known as placenta. The organization or configuration of these placenta or ovules on the ovary wall is referred to as placentation.

1.0Types of Placentation 

The different types of placentation in plants are classified based on the arrangement of ovules within the ovary:

Marginal Placentation: This type of placentation is characteristic of a monocarpellary gynoecium. The placenta forms a ridge along the ventral suture of the ovary, and ovules are arranged in two rows along this ridge. There is no distinct placenta present. Example: Pea (Leguminosae family).

 Axile Placentation: Axile placentation is observed in a multicarpellary, syncarpous gynoecium. The ovary is multilocular, and ovules are attached to the central axis. The number of chambers equals the number of fused carpels. Examples include China rose, lemon, and tomato.

 Parietal Placentation: This type occurs in a unilocular syncarpous ovary. Ovules develop on the inner wall of the ovary or its periphery. In some instances, the ovary may appear unilocular but can become bilocular due to the formation of a false septum or replum. Examples include Mustard and Argemone.

 Free Central/Central Placentation: Free central placentation is found in syncarpous gynoecium. The ovary is unilocular, lacking septa, and ovules are attached to the central axis. Examples include Primrose and Dianthus.

 Basal Placentation: In basal placentation, the ovary is unilocular, and the placenta develops at the base of the ovary. Typically, a single ovule is attached at the base of the ovary. Examples are Marigold and Sunflower (Asteraceae/Compositae family), as well as plants from the Gramineae/Poaceae family.

 Function of placentation: The function of placentation is to transfer nutrients, and water from maternal tissue to a growing embryo that present within the seed.