Racemose Inflorescence: Definition, Types, Differences, & Sample Questions

Inflorescence is defined as an arrangement of clusters of flowers on the floral or main axis. The major division of inflorescence is into two parts i.e., racemose and cymose depending on whether the apex gets converted into a flower or continues to grow. 

Also Check: Inflorescence

Key Terms: Flower, Inflorescence, Elongated Main- Axis, Shortened Main- Axis, Flattened Main- Axis, Cluster, Apex

---

What Is Racemose Inflorescence?

[Click Here for Sample Questions]

A racemose is a type of inflorescence in which the main axis grows indefinitely and does not end in a flower. As a result, it is also referred to as an indefinite or indeterminate inflorescence.

Some of the salient features of the racemose inflorescence are given below:

• The main axis is known as a peduncle, and the growth of the main axis is indefinite and continues to produce flower buds.
• Peduncles are monopodial.
• It is less common to see flowers arranged in groups.
• Flowers are born in acropetal succession, with older flowers on the periphery and younger ones on top.
• Flowers provide no protection to newly formed fruits.
• A flower is not always at the end of the peduncle.

Also Check: Morphology of Flowering Plants

Racemose

---

Types Of Racemose Inflorescence

[Click Here for Previous Year Questions]

The various types of racemose inflorescence are listed below. The racemose inflorescence is divided into various types based on the branching, length of the peduncle, and the presence or absence of pedicel:

Elongated Main-Axis

Elongated main axis is specified below: 

1. Raceme - A simple inflorescence in which the flowers are borne on short stalks of approximately equal length at equal distances along an elongated axis and open in succession toward the apex. 

Example: mustard (Brassica campestris) and radish (Raphanus sativus).

Compound raceme or panicle refers to when the main axis of the inflorescence is branched and lateral branches bear flowers in a simple raceme manner.

Examples: Mango(Mangifera indica ), Azadirachta indica (neem), etc.

2. Spike - The main axis remains elongated in this type of racemose inflorescence, and the lower flowers are older, i.e., open earlier than the upper ones, as in raceme, but the flowers are sessile. Amaranth (Amaranthus spp.), latjira (Achyranthes Aspera), etc. are example.

The spike of spikelets is another name for a compound spike. On the branched main axis, sessile flowers (spikelets) are present. Wheat, barley, sorghum, oats, etc. are examples.

Also Check: Crop Production

3. Spikelets - Each spikelet can have one or two several flowers (florets) attached to a central stalk called a rachilla. Spikelets are arranged in a spike inflorescence, which is made up of several to many spikelets that are combined in various ways along a central axis known as the rachis. Inflorescence of spikelets can be raceme, panicle, spike, or compound spike.

Raceme spikelet: Spikelets that grow on pedicels and are attached to the rachis (central axis). Festuca, Paspalum (crown grass), Echinochloa (barnyard grass), and other species are examples.

Panicle spikelet: Spikelets are attached to panicle branches rather than directly to the rachis. Avena, switchgrass, reed canary grass, Alopecurus (foxtails), and other species are examples.

Sessile Spikelet: A sessile spikelet that is attached directly to the rachis or panicle branches (compound spike) and lacks a pedicel. Hordeum, ryegrass, Triticum aestivum (Wheat), and others are examples.

4. Catkin - is a drooping spike with a modified central axis. It has unisexual sessile flowers that are arranged close together on the peduncle. Flowers have scaly bracts and inconspicuous petals. Morus alba (mulberry), Betula (birches), Salix (willows), etc. are examples.

Also Check: Monocot Dicot Plants Anatomy

5. Spadix - When a spathe covers a spike with a sheath-like covering, a spadix forms. Members of the Araceae, Musaceae, and Palmaceae, for example. This inflorescence is found primarily in monocotyledonous plants. 

They are joined in a spike inflorescence, which is composed of various spikelets that are combined in various ways along the main axis known as the rachis. Festuca, for example.

The main axis of the compound spadix is branched, and each branch bears sessile flowers. The entire inflorescence is surrounded by a thick boat-shaped spathe. For example, coconut.

Raceme & Panicle

Shortened Main Axis

The main axis grows slowly and is shortened in this case. Corymb & Umbel falls into this category:

1. Corymb - In this type of inflorescence, the length of the lower flower's pedicels is greater than the length of the upper flower's pedicels, resulting in all flowers appearing at the same level. When viewed from above, they have the general appearance of an umbrella.  A compound corymb is one that has the main axis branched in a corymbose pattern and flowers arranged in corymbs on each branch. Hawthorn is an example. 

Also Check: Plant and Tree 

2. Umbel - The main axis is shortened. The involucre of bracts (whorl) is present. Flowers emerge from the axil of bracts. Each flower has a pedicel that is the same length and spreads from a common point. 

It can be a simple umbel or a compound umbel, which is an umbel with branches, also known as an "umbel of umbels." The Apiaceae (Umbelliferae) family is known for its umbel inflorescence.

Simple Umbel plants include Centella Asiatica (Brahmi), Allium cepa (onion), Fatsia japonica (paper plant), Primula veris (cowslip), etc.

Compound umbels include Foeniculum vulgare (fennel), Daucus carota (carrot), Conioselinum pacificum (parsley), etc.

Umbel & Compound Umbel

Flattened Main Axis

The main axis is Flattened in this case. Capitulum falls into this category:

1. Capitulum - In this type of inflorescence, the main axis becomes suppressed and flat, and the flower becomes sessile, or without talk, allowing them to form crowded patterns on the flat surface of the receptacle. 

These florets are arranged in a centripetal pattern on the receptacle, which means that the outer flowers are older and open earlier than the inner ones.

Also Check: Difference Between Monocot and Dicot Stem

Inflorescence

---

Difference Between Cymose And Racemose Inflorescence

[Click Here for Sample Questions]

The main difference between racemose and cymose inflorescence is described below:

Also Check: Asexual Reproduction In Plants

---

Things To Remember

• A Racemose is a type of inflorescence in which the main axis continues to grow indefinitely and does not terminate in a flower.
• The simple inflorescence is classified into two types: Racemose Inflorescence & Cymose Inflorescence
• Aside from these two, inflorescence can be classified into three types: Hypanthodium, Cyathium, & Verticillaster.
• The different types of racemose inflorescences are based on an elongated main axis: Raceme, Spike, Spikelets, Catkin, & Spadix; Based on a shorter main axis: Corymb & Umbel; Based on a flattened main axis: Capitulum.

---

Important PYQs Based on Racemose Inflorescence

1. Radial symmetry is found in the flowers of... [NEET 2016]
2. The inflorescence in Ocimum is... [JIPMER 2004]
3. Cymose inflorescence is present in... [NEET 2012]
4. Inflorescence is racemose in... [NEET 2013]