Placentation in plants refers to the arrangement of the distribution of ovules and the placentas present inside a plant ovary.
Based on its type of arrangement, the placentation divides the plants into five major categories – namely axial placentation, marginal placentation, parietal placentation, basal placentation, and superficial placentation.
Axial placentation:
The placenta are formed in the center where the walls of the carpels join.
The type of ovary can be bicarpellary or multicarpellary and syncarpous ovary.
Example: Rutaceae.
Marginal placentation:
The ovules can be found where the margins of two carpels meet.
The type of ovary can be unilocular and monocarpellary ovary.
Example: Fabaceae.
Parietal placentation:
This type of placentation has its carpels fusion only at the margins and the ovules are beared by the placenta at the place of two-carpel fusion.
The type of ovary can be unilocular, multicarpellary and syncarpous ovary.
Example: Cucurbitaceae.
Basal placentation:
The development of placenta can be seen on the receptacle and only a single ovule is present at the base of the ovary.
The type of ovary can be unilocular, bicarpellary and syncarpous ovary.
Example: Poaceae.
Superficial placentation:
The development of placenta can be seen on the inner partition wall where it bears ovules.
The type of ovary can be multilocular and multicarpellary.
Example: Nymphaeaceae.
The various types of placentation that are found in flowering plants are axial placentation, marginal placentation, parietal placentation, basal placentation, and superficial placentation which have various types of placental arrangement and types of ovaries.