Parietal placentation is found in Brassicaceae (Cruciferae). Here, carpels are fused only by their margins, and placentas then appear as internal ridges on ovary wall.

In marginal type, the placenta develops along the junction of two carpels in a unilocular ovary, e.g., Pea.

In axile placentation, margins of carpels fold inwards and fused in the ovary centre to form a single central placenta. 

In basal placentation, the ovules are few or reduced to one and present at the base of the ovary. The ovule, when solitary, often fills the ovary cavity and is unilocular e.g., Compositae.