Placentation refers to the arrangement of ovules inside the ovary. It is of five basic types.

$(A)$ Marginal placentation:

The ovary in which the placenta forms a ridge along the ventral suture of the ovary and the ovules develop on two separate rows is known to have marginal placentation. This type of placentation is found in peas.

$(B)$ Parietal placentation

When the ovules develop on the inner walls of the ovary, the ovary is said to have parietal placentation.

$(C)$ Axile placentation

In axile placentation, the placenta is axial and ovules are attached to it. Examples include China rose, lemon, and tomato.

$(D)$ Basal placentation

The ovary in which the placenta develops from its base and a single ovule is found attached to the base is said to have basal placentation. It is found in marigold and sunflower.

$(E)$ Free central placentation

In free central placentation, the ovules develop on the central axis while the septa are absent. This type of placentation is found in Dianthus and primrose.