[Biology Class Notes] on Cymose Inflorescence Pdf

The inflorescence is a particular fashion in which a cluster of flowers is arranged on the stem or the floral axis. Morphologically, it is the part that is modified from a shoot in angiosperms where flowers are formed. It can also be defined as the reproductive part of the plant that bears the group or cluster of flowers in a particular fashion. The stem that holds the inflorescence is termed the peduncle and the one which is the major axis that holds the inflorescence or other branches is called the rachis. The stalk of each flower in an inflorescence is called a pedicel.

 

There may be a flower that is not part of the inflorescence, that stands as a solitary flower and the flowers in the inflorescence are referred to as florets. Flowers turn into fruits we already know and the stage at which it occurs in the inflorescence is known as infructescence. Inflorescence can either be simple or complex. Depending on this, there are various types of inflorescence–. The simple inflorescence is of two types–: Racemose inflorescence and Cymose inflorescence. The other types of inflorescence are Hypanthodium, Cyathium, and Verticillaster.

 

Types of Inflorescence

Simple Inflorescence

• Racemose–: It is a simple type of inflorescence in which the main axis continues to grow and flowers are borne laterally in an acropetal succession on the axis. As the stem or shoot continues to grow, this type of arrangement is also named as the indefinite Inflorescence. The arrangement of flowers is said to be in acropetal order and may at a time grow laterally to the main shoot (called peduncle). In racemose inflorescence, flowers are usually in a centripetal arrangement in which the young flowers are at the center or at the end of the stem and the older flowers will take the position at the bottom of the stem or peduncle. This type of arrangement occurs for a shorter period of time and flowers stay open for short intervals. These flowers or flowering plants can be a great example of racemose inflorescence; these are mustard, larkspur, snapdragon, etc. 

• Cymose–: It is another simple type of inflorescence in which the termination of growth of the main axis occurs and the flowers are borne in a basipetal succession. Thus, in this case, the main axis shows limited growth. As the growth of the main stem (peduncle) is hurt by the terminal flowers, this type of arrangement of flowers in an angiosperm is also called a definite fluorescence. This terminal flower at the outer end of the main stem is the major difference between the cymose and racemose inflorescence. The flower in these types of plants is the most dominant flower in the cymose plant and the younger plant starts to grow from the stem below the terminal flowers. The flowers in these angiosperms are in a bipedal sequence. The newly formed shoots from the bottom of the main stem (peduncle) and it is also got terminated by another terminating flower growing at the outer end of the newly formed shoot.

 

Other Inflorescence

• Hypanthodium: The main axis forms a cup-shaped structure that has a cavity which holds male and female flowers and a small apical opening.

• Cyathium: In this case, the involucre of bracts forms the cup-shaped structure. A sSingle flower is present in the middle surrounded by male flowers.

• Verticillaster: This type of inflorescence is seen in plants with opposite leaves. The two exiles of leaves give rise to two clusters of sessile flowers. Each cluster of flowers shows a dichasial cyme arrangement.

 

Types of Cymose Inflorescence

There are basically four main types–:

1. Monochasial Cyme: It is also called a uniparous cyme in which the main axis terminates in a flower and it produces one lateral branch from the base, which also terminates in a flower. Each lateral and subsequent branch gives rise to a lateral branch with a terminal flower. This type of cymose inflorescence is further divided into two types:

• Scorpioid: On both sides of the axis, lateral branches are developed. Example–: Sundew.

• Helicoid: Lateral branches form a helix structure by growing on the same side. Example:– Begonia.

2. Dichasial Cyme: It is also called a biparous cyme in which the terminal peduncle terminates in a flower. It grows into two lateral branches with terminal flowers. Subsequent branches also grow in a similar pattern. Example:– Jasmine.

3. Polychasial Cyme: It is also called a multiparous cyme because multiple branches arise at the base of the apical flower on the peduncle. The oldest flower is placed in the middle of the axis. Example:– Calotropis.

4. Cymose Capitulum: The peduncle is reduced to a circular disc in this type of inflorescence. Thus, the older flowers are at the center of the disc and the younger flowers grow at the periphery. This is also called a centrifugal arrangement. Example:– Mimosa, Acacia, etc.