What is the Difference Between Marginal and Parietal Placentation

The key difference between marginal and parietal placentation is that in marginal placentation, ovules are attached to a ridge made from the placenta at one of the margins of the ovary, while in parietal placentation, ovules are attached to the periphery of the ovary.

In flowering plants, ovules are located inside the ovary. Ovules attach to the ovary wall in different arrangements, and these arrangements are named placentation. In other words, placentation refers to the arrangement of ovules inside the ovary. Ovules attach to the flower’s placenta, which is an outgrowth of tissue shaped like a ridge through a stalk called the funiculus. Placentation plays a crucial role as it determines how seeds are positioned within the fruit. Moreover, placentation is a significant feature in plant taxonomy. There are five distinct forms of placentation in flowering plants, namely axile placentation, marginal placentation, parietal placentation, basal placentation, and superficial placentation.

CONTENTS

1. Overview and Key Difference
2. What is Marginal Placentation
3. What is Parietal Placentation
4. Similarities – Marginal and Parietal Placentation
5. Marginal vs. Parietal Placentation in Tabular Form
6. FAQ – Marginal and Parietal Placentation
7. Summary – Marginal vs. Parietal Placentation

What is Marginal Placentation?

Marginal placentation is a placentation seen in flowering plants. In marginal placentation, the placenta makes a ridge at one margin of the ovary. Then, the ovules attach to this ridge.

Peas are the most common example of this type of placentation. In pea plants, ovules are attached as a row on the ventral suture of the ovary. Fabaceae plants show marginal placentation, and it is one characteristic of this family of plants. Plants showing marginal placentation have an unilocular ovary or a one-chambered ovary. They have no septum in the ovary.

What is Parietal Placentation?

Parietal placentation is another type of placentation seen in flowering plants. In parietal placentation, ovules attach to the inner ovary wall. Similar to marginal placentation, parietal placentation is also seen in the unilocular ovary. But, due to the formation of a false septum, unilocular ovary can become bilocular later.

In parietal placentation, many placentae are attached to one locule; hence, parietal placentation shows a high ovule number. In other words, parietal placentation is associated with multi-ovulate ovaries. Normally, numerous ovules are present attached to one placenta. Parietal placentation is a characteristic property of the plant family Brassicaceae or Cruciferae.

What are the Similarities Between Marginal and Parietal Placentation?

• Marginal and parietal placentation are two of the five placentations seen in flowering plants.
• Both types are found in unilocular ovaries.
• They are characteristic properties in certain plant families.

What is the Difference Between Marginal and Parietal Placentation?

Marginal placentation is the type of placentation in which ovules are attached along the suture of the ovary, while parietal placentation is the type of placentation in which ovules are attached to the inner wall of the ovary. Thus, this is the key difference between marginal and parietal placentation. Furthermore, marginal placentation is a characteristic property of the family Fabaceae, while parietal placentation is a characteristic property of Brassicaceae or Cruciferae. The ovary has a single placenta in the marginal placentation type, while the ovary has two or more placenta in the parietal placentation type. Unlike marginal placentation, parietal placentation is associated with a high ovule number.

The infographic below presents the differences between marginal and parietal placentation in tabular form for side by side comparison.

FAQ: Marginal and Parietal Placentation

What are the different types of placentation in fruit?

The different types of placentation in fruit are axile placentation, marginal placentation, parietal placentation, basal placentation, and superficial placentation.

What is the difference between parietal and axile placentation?

The key difference between parietal and axile placentation is the location of ovules within the ovary. In parietal placentation, ovules are attached to the ovary wall, while in axile placentation, ovules are attached to the central column or axis within the ovary.

What are the types of placentation with examples?

• Axile Placentation: Ovules are attached to a central column or axis within the ovary. Examples include tomatoes and bell peppers.
• Marginal Placentation: Ovules are attached to the inner edge or margin of the ovary. Examples include peas and beans.
• Parietal Placentation: Ovules are attached to the inner wall of the ovary. Examples include lilies and poppies.
• Basal Placentation: Ovules are attached at the base of the ovary. Examples include sunflowers and violets.
• Superficial Placentation: Ovules are spread out on the inner surface of the ovary. Examples include pomegranates and passionflowers.

Summary – Marginal vs. Parietal Placentation

Placentation refers to the way of ovule attachment on the wall of the ovary. In marginal placentation, ovules are attached to a ridge at one of the margins of the ovary. In parietal placentation, ovules are attached to the inner wall of the ovary. Numerous ovules are attached to one placenta, and there are two or more placenta in the ovary of parietal placentation. However, there is a single placenta in the ovary of marginal placentation. So, this summarizes the difference between marginal and parietal placentation.

Reference:

1. “Placentation in Flowering Plants.” Study.Com.
2. Shivaprakash, K. Nagaraju, and Kamaljit S. Bawa. “The Evolution of Placentation in Flowering Plants: A Possible Role for Kin Selection.” Frontiers.

Image Courtesy:

1. “Gynoecium morphology placentation marginal longitudinal section” By Michael G. Simpson. Redrawn and color: User:RoRo – Simpson (2005) Plant Systematics. (Public Domain) via Commons Wikimedia
2. “Gynoecium morphology placentation parietal-1 cross section” By Michael G. Simpson. Redrawn and color: User:RoRo – Simpson (2005) Plant Systematics. (Public Domain) via Commons Wikimedia