What is the Difference Between Capitulum and Hypanthodium

The key difference between capitulum and hypanthodium is that capitulum is a racemose inflorescence while hypanthodium is a cymose inflorescence.

The inflorescence is a cluster of flowers on a stem. Racemose and cymose are two types of inflorescence. Flowers branch laterally on the floral axis in racemose inflorescence. The floral axis continues to grow, and flowers grow in an acropetal pattern. Capitulum is a type of racemose inflorescence. In cymose inflorescence, flowers act as the terminating point of the floral axis, and they grow in a basipetal pattern. Hypanthodium is a cymose type of inflorescence. In racemose inflorescence, the main axis grows indefinitely, while in cymose inflorescence, the main axis has limited growth.

CONTENTS

1. Overview and Key Difference
2. What is Capitulum
3. What is Hypanthodium
4. Similarities – Capitulum and Hypanthodium
5. Capitulum vs Hypanthodium in Tabular Form
6. Summary – Capitulum vs Hypanthodium

What is Capitulum?

Capitulum is a type of racemose inflorescence. It shows an arrangement of flowers at the base of the floral axis. It is an example of pseudanthium. Capitulum exists as a short, compact cluster of flowers. The individual flowers found in each cluster are known as florets. Capitula take various forms; therefore, the florets may be on the smaller side or larger side. A few examples of florets appearing on the smaller side are cauliflower, broccoli, and clovers. Some examples of florets seen on the larger side are daisies, sunflowers, thistles, and dandelions. In capitulum, thousands of flowers form a single structure. Capitula have two types of florets as disc florets and ray florets. Disc florets are in the center, and they are actinomorphic, and the corolla fuses to a tube. Ray florets are in the periphery; they are zygomorphic, and the corolla has one large lobe.

Capitula are superficially indistinguishable from a flower since they possess multiple flowers. Therefore, they have a reduced reproductive unit that may function in pollination compared to a single flower. Florets that are smaller are hardly recognizable since organs like carpels and stamen cannot be associated with an individual flower. However, larger florets are recognizable as single flowers even if they fuse together.

What is Hypanthodium?

Hypanthodium is a cymose inflorescence. The receptacle in this type is a hollow spherical-shaped structure with a cavity inside. It is formed by the fusion of stems of cymes near each other. These spherical receptacles are closed structures with a fleshy nature having a tiny opening at the apex. Therefore, it is exposed to the exterior. Small flowers are present on the inner surface of the receptacles. There are three types of unisexual flowers: male, sterile female, and fertile female flowers.

Hypanthodium flowers are flask-shaped and possess fleshy receptacles. These flowers have narrow canals with terminal pores in one end. The canals are lined by hair-like structures, while pores are covered in scales. Internally, the receptacles contain male flowers towards the pores, and the female flowers are towards the base area. Sterile flowers occur between the two types. Examples of hypanthodium inflorescence are in the genus Ficus of the family Moraceae. A few examples are banyan, fig, and peepal.

What are the Similarities Between Capitulum and Hypanthodium?

• Capitulum and hypanthodium are types of inflorescences.
• Both contain receptacles.

What is the Difference Between Capitulum and Hypanthodium?

Capitulum is a racemose inflorescence, while hypanthodium is a cymose inflorescence. Thus, this is the key difference between capitulum and hypanthodium. Moreover, the receptacle in capitulum is a broad, flattened upright column that becomes fleshy, while the receptacle in hypanthodium is flask-shaped and becomes fleshy. Also, a whorl surrounding the flowers known as the involucre occurs at the base of capitula while there is no involucre in hypanthodia. In addition, capitulum contains bisexual flowers while hypanthodium consists of unisexual flowers with a distinct distribution.

The below infographic presents the differences between capitulum and hypanthodium in tabular form for side by side comparison.

Summary – Capitulum vs Hypanthodium

Inflorescences are two types as racemose and cymose. Capitulum is a type of racemose, while hypanthodium is a type of cymose. Capitulum exists a short, compact cluster of flowers. They are located at the base of the floral axis. Hypothandium consists of three cymes and is located in the floral axis. Capitulum contains a broad, flattened receptacle, and hypanthodium contains a flask-shaped receptacle. So, this is the summary of the difference between capitulum and hypanthodium.

Reference:

1. “Hypanthodium – Definition, Examples, Flowers, Cyathium.” BYJUS.
2. Minorsky, Peter. “Auxin Affects Capitulum Pattern Formation.” Plantae.

Image Courtesy:

1. “Flower July 2011-2 1 cropped” By Alvesgaspar cropped by Davefoc – (CC BY-SA 3.0) via Commons Wikimedia
2. “Flower morphology – longitudinal section showing achene formation and hypanthium in Rosa-01” By RoRo – Own work (CC0) via Commons Wikimedia