Inflorescence: Racemose and Cymose, Practice problems, FAQs

What is the purpose of a flower in the plant body? Flowers help in the process of reproduction in angiosperms, right? For sexual reproduction to happen, pollination is an important step in flowering plants. For pollination by different biotic agents, it is often necessary that the flowers are prominently visible to the animals and attract them. The arrangement of flowers on the main axis of the plant is very important in this aspect. 

You must have seen that some flowers like the Hibiscus are large and attractive and are borne singly on the branches whereas others like Bougainvillea are borne in clusters. What do you think, whether the arrangement of these single flowers or the clustered ones, is random or does it follow any pattern? Are all clustered flowers arranged the same way? If not then what are these different types of arrangements of flowers on the floral axis? Let us understand more about all this with the help of this article.

Table of contents

• Inflorescence
• Racemose inflorescence
• Cymose inflorescence
• Special inflorescences
• Practice problems
• FAQs

Inflorescence

Flower is a reduced shoot which is the reproductive organ of a plant and it develops either from an axillary or from a terminal bud. A floral axis or peduncle can have multiple flowers borne on it. Flowers can be borne singly or in clusters. If borne singly, flowers are said to be solitary. Flowers borne in clusters are arranged in different patterns on the peduncle. The arrangement of flowers on the floral axis is known as inflorescence.

Inflorescence can primarily be of two types:

• Racemose inflorescence
• Cymose inflorescence

                                                Fig: Types of inflorescences

Racemose inflorescence

In racemose inflorescence, there is indefinite growth of the main axis as it does not terminate into a flower. The flowers arrangement is in acropetal order, i.e, older flowers lie at the base and younger flowers at the apex. Example: Gulmohar

                                  Fig: Racemose inflorescence in Gulmohar

Racemose inflorescence can be of certain types which are listed below:

Simple racemose inflorescence

Racemose inflorescence is said to be simple if the peduncle is unbranched. This can be of the following types -

Simple raceme

The main axis is unbranched, elongated and bears flowers laterally in an acropetal succession in simple raceme. There are many pedicellate flowers produced. Example: Crotalaria.

            Fig: Raceme inflorescence in Crotalaria

Corymb

In corymb, the peduncle is short. Flowers are pedicellate. The lower flowers have longer stalks than the upper ones. All flowers lie at the same level. Example: Iberis (candytuft).

                               Fig: Corymb inflorescence in Candytufṭ

Umbel

In this type of inflorescence the peduncle is short and condensed. The flowers arise in clusters from the same point. The pedicels of all the flowers are the same length. A whorl of bracts known as involucre may be present at the base. Example: Onion

                                       Fig: Umbel inflorescence in onion

Spike

Main axis is elongated in a spike. Sessile flowers are arranged in acropetal fashion. Examples: Amaranthus, Callistemon (bottlebrush) etc.

                      Fig: Spike inflorescence in bottlebrush

Catkin

It is similar to a spike but has a long pendulous axis. Flowers borne on the main axis are unisexual and sessile. Example: Mulberry

                     Fig: Catkin inflorescence

Spadix

It is a spike with a long and fleshy peduncle. The peduncle is covered with one or more coloured bracts called spathe. The male and female flowers are closely packed together. The base has female flowers while the male flowers occupy the upper region of the peduncle. Sterile florets lie in the middle. The spathe becomes tubular at the base. Examples: Maize, banana, Colocasia, etc.

                  Fig: Spadix inflorescence in banana

Head/Capitulum 

The peduncle is flattened to form a disc-like receptacle. It bears many sessile flowers known as florets. The ray florets lie at the periphery and have tongue shaped corolla or petals. The disc florets lie on the receptacle and are surrounded by a whorl of bracts called involucre. Example: Sunflower.

                                    Fig: Head / Capitulum inflorescence 

Compound racemose inflorescence

It is the type of racemose inflorescence in which the peduncle is branched and the branches are borne on the mother peduncle in an acropetal fashion. It is of the following types -

Compound raceme

Pedicellate flowers are borne acropetally on the lateral branches of an elongated peduncle.

Compound spike

Sessile flowers are borne over branches of elongated peduncles.

Compound spadix

The unisexual sessile flowers are borne over the branches of the peduncle of a spadix. The whole inflorescence is covered by a spathe and the individual branches may or may not be covered by spathes known as spathellae.

Compound corymb

A mother corymb bears a number of daughter corymbs.

Compound umbel

A number of daughter umbels known as umbellules are formed from a single point which has an involucre of bracts at its base. Daughter involucres of bracts or involucels can be seen at the base of each umbellule.

                        Fig: Compound umbel

Compound capitulum

In this, the flattened receptacle of the mother capitulum bears many daughter capitula.

Cymose inflorescence

The primary floral axis terminates into a flower and hence has definite growth. Growth continues through lateral buds. Flowers are arranged in basipetal succession, that is, the older flowers lie at the apex and the younger flowers below it.

                       Fig: Cymose inflorescence

Types of cymose inflorescence are as follows:

Solitary cyme

A single, axillary or terminal flower is produced on the floral axis. Examples: Terminal: Datura and Axillary: Hibiscus

                                                      Fig: Solitary cyme

Monochasial cyme 

The main floral axis or peduncle terminates into a flower. A single lateral branch emerges at a time which terminates into a flower. Example: Drosera, Freesia etc.

                         Fig: Monochasial cyme

Dichasial cyme

In dichasial cyme, the main axis terminates into a flower. Two lateral branches are produced, each of which also terminate with a flower. Example: Jasmine

                                Fig: Dichasial cyme

Polychasial cyme

The main/mother axis terminates into a flower but gives rise to more than two lateral branches. Each lateral branch behaves like the mother axis. Example: Calotropis

                                   Fig: Polychasial cyme

Special inflorescences

Hypanthodium

It is a special inflorescence formed by the condensation of three types of cymose inflorescence within a flask-shaped fleshy receptacle. The inflorescence has a pore lined by scales which leads to a canal. The canal has inwardly directed hair and male flowers lie towards the pore, female flowers at the base and neuter or gall flowers in between the two. This is a characteristic of the Ficus species.

                                Fig: Hypanthodium inflorescence

Verticillaster

It is a raceme of whorls of cymose flowers that develop in the axils of opposite leaves. Each whorl has two clusters each of which possess 3-9 flowers formed of a biparous cyme having uniparous branching. The peduncle is reduced such that flowers appear to develop from the axil of the leaves. Due to overcrowding the two opposite clusters seem like a single whorl or verticil. This is seen in Salvia, Ocimum, etc.

                                          Fig: Verticillaster inflorescence

Cyathium

It is a type of condensed cymose inflorescence which appears like a single flower borne on a conical receptacle having green involucre of 4-5 bracts with nectariferous glands. The receptacle has a single centrally placed female flower surrounded by centrifugally placed male flowers. The flowers bear pedicels and are achlamydeous (lack both calyx and corolla) and unisexual. This indicates that flowers have a single essential organ, pistil in female flowers and stamens in male flowers. The essential organ is connected to the pedicel. This type of inflorescence is seen in Euphorbia, Anthostemma, etc.

                                            Fig: Cyathium inflorescence

Practice problems

Q 1. Which of the following statements is incorrect regarding cymose inflorescence?

a. Growth occurs through lateral buds.
b. Flowers are borne in a basipetal succession.
c. Cymose inflorescence is seen in jasmine.
d. Growth of peduncle is indefinite.

Answer:  In cymose inflorescence, the primary floral axis terminates into a flower and hence has definite growth. Growth continues through lateral buds and the flowers are arranged in basipetal succession with older flowers at the apex and the younger flowers below it.

Thus, the correct option is d.

Q 2. Terminal solitary cyme is seen in 

a. Hibiscus
b. Datura 
c. Both 
d. None

Answer:  A solitary cyme is a cymose inflorescence in which a single, axillary or terminal flower is produced on the floral axis which has definite growth and flowers develop in basipetal succession.

A terminal flower develops in Datura whereas in Hibiscus flowers are axillary in position.

Thus, the correct option is b.

Q 3. Which of the following statements best describes an umbel?

a. The peduncle is short and bears pedicellate flowers at the same level with lower flowers having longer stalks than the upper ones.
b. It is a spike with a long and fleshy peduncle covered with one or more coloured bracts called spathe.
c. In this type of inflorescence the peduncle is short and condensed and pedicellate flowers arise in clusters from the same point on the peduncle. The pedicels of all the flowers are the same length. 
d. The peduncle terminates into a flower and a single lateral branch emerges at a time which terminates into a flower.

Answer: An umbel is a type of simple racemose inflorescence in which the peduncle is short and condensed. The flowers arise in clusters from the same point and bear pedicels of the same length. A whorl of bracts known as involucre may be present at the base. Example: Onion.

Thus, the correct option is c.

Q 4. Differentiate between racemose and cymose inflorescence.

Answer: 

FAQs

Q 1. Do inflorescences develop into fruits?
Answer: Fruits that develop from inflorescences are said to be composite fruits or an etario of fruitlets. For example, jackfruit, custard apple, etc.

Q 2. What is the significance of an inflorescence?
Answer: Inflorescences directly affect the reproductive success of a plant by increasing the chances of pollination as inflorescences have flowers in clusters which are more conspicuous.

Q 3. Which floral family shows cymose inflorescence?
Answer: Members of the Solanaceae family such as Solanum nigrum exhibit cymose inflorescence. A cymose inflorescence is one in which the growth of the main axis is determinate and it terminates into a flower. Further growth occurs with the help of lateral buds and new flowers develop in a basipetal fashion.

Q 4. What type of fruit develops from a hypanthodium?
Answer: A hypanthodium develops into a syconus fruit such as fig in which the fleshy edible part is the flask shaped receptacle.

Youtube link: 

https://youtu.be/5sOsDXjM_T8 (05:32 - 11:40)

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