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. e.g peas.

(B) Parietal placentation:
When the ovules develop on the inner walls of the ovary, the ovary is said to have parietal placentation. Ovary is one chambered but it becomes two chambered due to the formation of the false septum. e.g mustard.

(C) Axile placentation:
In axile placentation, the placenta is axial and ovules are attached to it. e.g China rose.

(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. e.g marigold.

(E) Free central placentation:
In free central placentation, the ovules develop on the central axis while the septa are absent. e.g Dianthus.