Placentation of flowering plants - SS2 Biology Lesson Note

Placentation refers to the arrangement and attachment of ovules within the ovary of a flowering plant. It plays a crucial role in seed development and is classified into various types based on the positioning of ovules within the ovary. Here are some common types of placentation in flowering plants:

1.       Marginal Placentation: In marginal placentation, the ovules are attached to the inner wall or margin of the ovary. A single elongated placenta runs along the margin of the ovary, and the ovules are attached to it. Examples of plants with marginal placentation include members of the Malvaceae family, such as hibiscus.

2.       Axile Placentation: Axile placentation occurs when the ovules are attached to a central column or axis within the ovary. The ovary is divided into two or more chambers (locules), and the placenta is located along the central axis. Examples of plants with axile placentation include tomatoes, lilies, and peppers.

3.       Free Central Placentation: In free central placentation, the ovules are attached to a central column or stalk called a "free central placenta." The ovary is not divided into separate chambers, and the ovules are attached directly to the central column. Examples of plants with free central placentation include members of the Ranunculaceae family, such as buttercups.

4.       Parietal Placentation: Parietal placentation occurs when the ovules are attached to the inner wall (parietal region) of the ovary. The ovary may have one or more chambers, and the ovules are attached along the inner wall. Examples of plants with parietal placentation include members of the Brassicaceae family, such as mustard plants.

5.       Basal Placentation: Basal placentation is characterized by the attachment of ovules at the base or bottom of the ovary. The ovary has a single chamber, and the ovules are attached near the base. Examples of plants with basal placentation include members of the Malvaceae family, such as mallows.

6.       Apical Placentation: Apical placentation occurs when the ovules are attached at the apex or top of the ovary. The ovary has a single chamber, and the ovules are attached near the top. Examples of plants with apical placentation include members of the Lamiaceae family, such as mint plants.

(toppr.com)

It's important to note that some plants may exhibit variations or combinations of different types of placentation. The type of placentation can have implications for seed development, fruit structure, and dispersal mechanisms. It also contributes to the overall diversity and reproductive strategies of flowering plants.