Placentation in flower of flowering plant

 

In the flowering plants, the ovule is located inside the ovary in a flower. The ovules are arranged inside the ovary in different manners. The arrangement of ovules inside the ovule is referred to as Placentation.

The ovule is attached with the ovary by a stalk called Funicle.The ovule is also called megasporangium.

The arrangement of seed in a fruit depends on the type of placentation. There are different types of placentation:

Marginal Placentation

This type of placentation can be in the case of  monocarpellary and unilocular gynoecium. or  one carpel. This type of placentation is mostly found in the family Leguminosae or Fabaceae. In this type of placenta, the ovules are arranged on the ridge. Examples of this placentation are: Pea, Gram, Mung, etc.

Parietal Placentation

This type of placentation, the multicarpellary gynoecium having  two or more carpels. Carpels are united to form only one chamber. Various ovules are arranged on the inner surface  of the ovary in one-chamber or  two-chamber. Both chambers are separated by the  false septum .

This type of placentation is found in mustard, Argemone and other members of the Brassicaceae family.

Axile Placentation

This type of placentation can be found when the gynoecium is multicarpellary and  syncarpous.

The ovary has  many chambers and the number of chambers corresponds to the number of carpels. The various types of ovules are arranged at the  central axis of ovary So, it is called axile placentation.

This type of placentation is found in Petunia  China-rose Althaea, tomato, lemon, etc. This is one of the most common types of placentations in plants.

Free Central Placentation

This type of placentation is found in  multicarpellary gynoecium.

More chambers are found in the early stage of the ovary which are combined later on  and the ovary becomes unilocular therefore  it can be said that septa are absent. The ovules are borne at the center of the ovary, which is quite separate from the ovary wall. This type of placentation is found in Dianthus, Primula, etc

Basal Placentation 

In this type of placentation, the gynoecium is also  multicarpellary. The ovary is unilocular.  A single ovule develops at the base of the ovary. The placenta is placed on the tip of the thalamus at the floor of the ovary.

This type of placentation is found in sunflower, rice, wheat, maize, etc.

Superficial Placentation

In this type of placentation, the gynoecium is multicarpellary, syncarpous and multilocular.

The ovules can be seen  around the inner surface of the partition walls and many ovules are borne on the ovary  without any specific order. This type of placentation is found in Waterlily.

Significance of placentation

It helps in the transfer of nutrients, respiratory gasses, and water from maternal tissue to the developing embryo.  It protects the developing ovules.

It also helps in the elimination of waste from the embryo.