Difference between Anatropous and Orthotropous Ovule

Structure of an Ovule

An ovule or megasporangium is a small female reproductive structure. It is attached to the placenta by a stalk-like structure called the funicle. The junction between the funicle and ovule is called the hilum. Each ovule has a protective covering called the integuments. There is a small opening at the tip of the ovule which is not covered by integuments. It is known as the micropylar end. Opposite to this is the basal part called chalaza.

Based on the position of the ovule and the micropyle structure, the ovules can be divided into –

  • Amphitropous
  • Anatropous
  • Orthotropous
  • Hemianatropous
  • Camypylotropous

Anatropous Ovule

Anatropous Ovule

In an anatropous structure, when the ovule is inverted, the micropyle tip faces the placenta. Here, the chalazal end will be in the upper position, and the micropylar end will lie near the funicle. It is the most common type of ovule orientation seen in most plants.

Orthotropous Ovule

Here, the ovule appears as a straight structure and is devoid of any curvature. The micropyle, nucleus, chalaza and funicle all lie in the same line. The micropyle forms the apex region. The chalaza and funicle form the basal region. This type of ovule is less abundant when compared to anatropous.

Difference between Anatropous and Orthotropous Ovule

Anatropous Ovule

Orthotropous Ovule

This ovule is a completely curved or inverted structure.

In this ovule, the micropylar end, chalaza and funicle all lie in the same line.

Here, the body of the ovule fuses with the funicle.

Here, the funicle does not fuse.

The micropyle is found at the bottom.

The micropyle is found at the apex.

This type of ovule is seen in most monocots and dicots.

This is mostly observed in plant families like Piperaceae and Polygonaceae.

The anatropous ovule is the most common type of ovule orientation.

The orthotropous ovule type is less abundant compared to anatropous.

Frequently Asked Questions on

What is an amphitropous ovule?

The amphitropous ovule is a partly inverted structure. If anatropous is a 180-degree inversion, then amphitropous is 90°. Examples – Poppy, Tridax and Lemna.

What is an ovary and ovule in a plant structure?

The basal enlarged part of the pistil is the female reproductive part called the ovary. The ovary contains one or more ovules, which develop into seed after fertilisation. The number of ovules in an ovary varies with species.

What is a micropyle?

The micropyle is a small opening near the hilum of the ovule. It allows the male gametophyte to enter the ovule. They also play a vital role in seed germination. Usually, the radicle of a seedling emerges from the micropyle.

Further Reading:

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