The ovules are attached on ovary walls on one or more cushion called placenta. The arrangement of ovule within ovary wall is known as placentation.
There are different types of placentation
- Marginal placentation: The placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on the ridge. Example: Peas
- Axile placentation: The placenta is axial and the ovules are attached to the multilocular ovary. Example: China rose, lemon and orange.
- Parietal placentation: In this type of placentation, the ovules develop on the inner wall of the ovary. Ovary has a single chamber but appears to be double-chambered because of the formation of a false septum. Example: Mustard and argemone.
- Free central placentation: The ovules are borne on the central axis. The septum is absent in this type of placentation. Example: Dianthus and primrose.
- Basal placentation: In this type of placentation, the placenta is situated at the base of the ovary and a single ovule is attached to it. Example: Sunflower.
- Apical placentation: where one or few ovules develop at the top of a simple or compound ovary.