[Biology Class Notes] on Racemose Inflorescence Pdf for Exam

Flowers are known to be reproductive parts of plants, they have different attractive colors, which attract pollinators for pollination. Flowers can be present in solitary form or cluster form. Clustered forms of flowers can be found arranged on branches different from the other branches of the plant. So these clusters of flowers are called inflorescence and individual flowers in it are known as florets. Inflorescence are of various type on the basis of following categories:

1. Number and position of flowers

2. Sequence of flower development and

3. The nature of inflorescence branching

Racemose Inflorescence

It is a kind of inflorescence were the axis of the inflorescence has unlimited growth.  Here flowers are arranged in an 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 pedunculated.

Characteristic feature of Racemose Inflorescence:

1. Main axis is known as peduncle and the main axis growth is indefinite and continues to produce flower buds.

2. Peduncle is monopodial in nature.

3. Flowers grouping is less common

4. Flowers are born laterally in acropetal succession, older flowers are at the periphery and younger ones are at the top.

5. Fruits which are newly formed are not protected by flowers.

6. The peduncle seldom always terminates in a flower.

Diagramatic Representation of Racemose Inflorescence:

( soon)

Types of Racemose Inflorescence:

1. Racemose inflorescence is further divided into different types on the basis of growth of the main axis. On the basis of elongation of main axis racemose inflorescence are divided into five types based on their branching, length of peduncle and presence or absence of pedicel i.e a small stalk that bears flower:

1. Raceme: When flowers with pedicel are arranged in an acropetal manner. Example: mustard (Brassica campestris),  radish (Raphanus sativus).

2. Spike: When flowers without pedicel are arranged in an acropetal manner. Example: amaranth (Amaranthus spp.), latjira (Achyranthes aspera), etc.

3. Spadix: When a spike is covered by a sheath-like covering by a spathe it becomes a spadix. Example:members of Araceae, Musaceae and Palmaceae. This type of  inflorescence is found mainly only in monocotyledonous plants.

4. Spikelets: Under this inflorescence each spikelet may bear one to several flowers i.e florets and they are attached to a central stalk known as rachilla. They are attached in a spike inflorescence and this spike is composed of various spikelets which are combined in various different  manners on a main axis called the rachis. Example: Festuca.

Further This Spikelets are Differentiated into Various Categories They are:

Raceme Spikelet: In raceme spikelets, spikelets are born on pedicles and get attached to rachis i.e central axis. Examples are: crown grass(Paspalum).

Panicle Spikelet: In panicle spikelets, spikelets  are not directly attached to the rachis, instead they  are attached to panicle branches. Examples: Avena, switchgrass, etc.

Spike Spikelets: In Spike spikelets, spikelets are sessile in nature and they are directly attached to rachis or panicle branches i.e compound spikes. Example: Hordeum, Triticum aestivum(wheat), etc.

5. Catkin: It  is a kind modified spike with a long and drooping axis having unisexual flowers, e.g., mulberry (Moras alba), birch (Betula spp.), oak (Quercus spp.), etc.

2. Racemose Inflorescence Based on Shortened Main Axis:

1. Corymb: In this type of inflorescence, the length of pedicels of the lower flower is more than the length of pedicels of upper ones, so that all flowers come at the same level. Their general appearance is the same as an umbrella when we see them from the top. Example: Hawthorn.

2. Umbel: Under this inflorescence pedicellate flower in which the flower originates from the same place reaches the same level. Example: Waxflower.

3. Racemose Inflorescence Based on Flattened Main Axis:

1. Capitulum: In this type of inflorescence the main axis becomes suppressed, flat and the flower becomes sessile i.e without talk so that they can make  crowded patterns together on the flat surface of receptacle.  These florets are arranged in a centripetal manner on the receptacle, i.e., the outer flowers are older and open earlier than the inner ones.

Further These Florets are Divided into two Types:

1. Ray florets

2. Disc florets

Terms Regarding Racemose Inflorescence:

1. Acropetal Succession: It is a kind of  arrangement of flowers on the pedicel in such a way that the new flowers and buds are at the top and the older flowers are at the bottom.

2. Pedicel: It is a kind of small stalk-like structure.

3. Compound Spadix: Under this main axis is branched and each branch bears sessile flowers.