Differences Between Cymose and Racemose Inflorescence
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.
FAQs on Cymose Inflorescence: Types and Significance
1. What is a cymose inflorescence?
In a cymose inflorescence, the main floral axis (peduncle) ends in a flower, which limits its growth. This is why it's called a determinate inflorescence. New flowers develop from lateral buds below the terminal flower, leading to a sequence where the oldest flower is at the top (or center) and the youngest ones are at the base. This arrangement is known as basipetal succession.
2. How is cymose inflorescence different from racemose inflorescence?
The main difference lies in the growth of the main axis. In cymose, the main axis stops growing after forming a flower (determinate). In racemose, the main axis continues to grow and produce flowers laterally (indeterminate). This leads to opposite arrangements: cymose has older flowers at the top (basipetal), while racemose has older flowers at the bottom (acropetal).
3. What are the main types of cymose inflorescence?
Cymose inflorescence is mainly divided into four types based on the branching pattern:
- Monochasial Cyme: The main axis ends in a flower, and only one lateral branch develops at a time. Examples include Sundew and Drosera.
- Dichasial Cyme: The main axis ends in a flower, and two lateral branches develop below it. Examples include Jasmine and Bougainvillea.
- Polychasial Cyme: The main axis ends in a flower, and more than two lateral branches arise from the base. An example is Calotropis.
- Cymose Capitulum: The peduncle flattens into a disc, with the oldest flower in the center and younger ones on the periphery. An example is Acacia.
4. What are some common examples of plants with a cymose inflorescence?
You can find cymose inflorescence in many common plants. Some well-known examples include Jasmine, Bougainvillea, Calotropis (Madar), Hibiscus, and Teak. Observing these plants can help you see the characteristic pattern where the central or terminal flower is the oldest.
5. Why is cymose inflorescence also called a 'determinate' inflorescence?
The term 'determinate' refers to something that has a fixed limit. In a cymose inflorescence, the main stem's growth is determined, or stopped, because it terminates in a flower. Once the apical bud becomes a flower, it cannot grow any further. All subsequent growth must come from lateral buds, which is why the growth is considered finite or determinate.
6. How does the flower opening pattern in a cymose inflorescence work?
The flower opening pattern is called centrifugal. This means it starts from the centre and moves outwards to the periphery. Since the first, oldest flower is at the very tip of the main axis (the centre), it opens first. The younger, lateral flowers that develop on the sides open later. This is the direct opposite of a racemose inflorescence, which has a centripetal pattern (opening from the outside inwards).
7. What key features should I look for to identify a cymose inflorescence in a plant?
To identify a cymose inflorescence, look for these key features:
- A flower at the tip: Check if the main stem and its major branches end with a flower.
- Oldest flower at the top: Observe the cluster of flowers. The most mature or open flower should be at the centre or the highest point.
- Younger buds at the base: Look for smaller, unopened buds on the lower or outer branches of the flower cluster.
- Limited axis growth: The overall flower cluster often appears flattened or broad, as its vertical growth is limited.
