Inflorescence

Flowers are the reproductive parts of a plant. They are bright in colour and attractive to attract pollinators to it. Flowers can be present solitarily or in bunches or clusters. Clustered flowers can be found arranged on branches different from the other branches of the plant. These clusters of flowers are known as an inflorescence and each individual flowers in it are known as florets.

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Parts of an Inflorescence

An inflorescence has the following parts:

a)Peduncle: It is the main supporting stalk of the inflorescence.

b)Pedicle: It is the stalk of the individual flowers. Some flowers are sessile and do not have a stalk, they are directly attached to the peduncle.

c)Bracts: These are small green petal-like structures that are found near the peduncle. They are similar to the sepals in a flower.

d)Flower/Flowers: These rest atop the pedicle or the main stalk.

Learn more about Stem Structure here in detail.

Types of Inflorescence

It can be broadly classified based on the following:

1. Number and position of flowers
2. Sequence of flower development, and
3. The nature of inflorescence branching

They are commonly classified and studied under two categories: Racemose and Cymose inflorescence.

Racemose Inflorescence

In this type, the axis of the inflorescence has unlimited growth. The flowers are arranged in acropetal manner which means that the older flowers are present at the base while the younger ones are present towards the top. The individual flowers may be sessile or pedunculate.

(Source: Wikipedia)

The different types of the racemose inflorescence are:

• Raceme-Flowers with pedicel and are in an acropetal arrangement. Example: mustard
• Spike- Flowers without pedicel and are in an acropetal arrangement. Example: Barley
• Umbel- Pedicilate flowers in which the flowers originate from the same place and reach the same level. Example Waxflowers
• Corymb- Unlike in the Umbel, the corymb consists of pedicilate flowers where the length of pedicels of the lower flowers is more than that of the upper ones such that all the flowers come up to the same level. They have an umbrella appearance when seen from the top. Example: Hawthorn
• Spadix- when a spike is covered sheath-like covering by a spathe it becomes a spadix. Example: Banana
• Capitulum- It is actually a short spike where the flowers are directly placed on the peduncle and giving it a flower-like appearance. A smaller capitulum is called the head. Example: Dandelion, sunflower.

Learn more about Tissue System here in detail.

Cymose Inflorescence

(Source: Wikipedia)

In a cymose inflorescence, the axis has limited growth and the flowers are arranged in a basipetal manner which means that the older flowers are found towards the top and the younger ones towards the base of the axis.

The different types of the cymose inflorescence are:

• Monochasial/Uniparous– the main axis ends in a flower and has one lateral branch. Example: Drosera
• Dichasial/Biparous– The main axis produces a flower at the tip and produces two branches simultaneously at a lower level both of which also end in flowers. This pattern of branching is further repeated. Example: Dianthus
• Polychasial/ Multiparous– The main axis ends in a flower and at the same time it produces a number of lateral flowers around. The oldest flower lies in the centre and ends the main floral axis. Example: Calotropis
• Cymose Capitulum– In this case, the peduncle is reduced to form a disc-like structure. This disc bears sessile flowers with the oldest in the centre and the younger ones towards the periphery.

Solved Example for You

Q: Which of the following type of inflorescence has an axis with limited growth?

(a)    Drosera        (b) Sunflower

(c)     Mustard         (d) Barley

Sol. (a) Drosera

Axis with limited growth is seen in the cymose type. Drosera is a cymose inflorescence whereas the other three are racemose(have unlimited growth of axis). Therefore, the correct answer is option a.