What is racemose inflorescence definition structure and types
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:
Number and position of flowers
Sequence of flower development and
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:
Main axis is known as peduncle and the main axis growth is indefinite and continues to produce flower buds.
Peduncle is monopodial in nature.
Flowers grouping is less common
Flowers are born laterally in acropetal succession, older flowers are at the periphery and younger ones are at the top.
Fruits which are newly formed are not protected by flowers.
The peduncle seldom always terminates in a flower.
Diagramatic Representation of Racemose Inflorescence:
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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:
Raceme: When flowers with pedicel are arranged in an acropetal manner. Example: mustard (Brassica campestris), radish (Raphanus sativus).
Spike: When flowers without pedicel are arranged in an acropetal manner. Example: amaranth (Amaranthus spp.), latjira (Achyranthes aspera), etc.
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.
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.
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:
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.
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:
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:
Ray florets
Disc florets
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Terms Regarding Racemose Inflorescence:
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.
Pedicel: It is a kind of small stalk-like structure.
Compound Spadix: Under this main axis is branched and each branch bears sessile flowers.
FAQs on Racemose Inflorescence in Flowering Plants
1. What is racemose inflorescence?
A racemose inflorescence is a type of inflorescence in which the main axis continues to grow and flowers are arranged in an acropetal order. In this arrangement:
- The main axis is indeterminate (it does not end in a flower).
- Flowers are borne laterally on the axis.
- The youngest flowers are at the top and older ones at the base.
This type of inflorescence is common in many flowering plants and contrasts with cymose inflorescence.
2. What are the main characteristics of racemose inflorescence?
The main characteristics of racemose inflorescence include continuous growth of the main axis and acropetal arrangement of flowers. Key features are:
- Indefinite growth of the main axis.
- Flowers arise laterally from the axis.
- Acropetal succession (older flowers at the base, younger at the apex).
- Often produces a large number of flowers.
These traits help in efficient pollination and seed production.
3. What is the difference between racemose and cymose inflorescence?
The main difference between racemose and cymose inflorescence lies in the growth of the main axis and flower arrangement. The differences are:
- Racemose: Main axis is indeterminate; flowers show acropetal order.
- Cymose: Main axis ends in a flower; flowers show basipetal order.
- Racemose: Younger flowers at the top.
- Cymose: Younger flowers at the base.
This distinction is important in plant morphology and classification.
4. What are the types of racemose inflorescence?
The types of racemose inflorescence are classified based on the branching pattern of the main axis. Major types include:
- Raceme – elongated axis with pedicellate flowers (e.g., mustard).
- Spike – elongated axis with sessile flowers (e.g., Achyranthes).
- Catkin – drooping spike with unisexual flowers (e.g., mulberry).
- Spadix – fleshy spike with a spathe (e.g., banana).
- Corymb – lower flowers have longer pedicels (e.g., candytuft).
- Umbel – flowers arise from a common point (e.g., coriander).
- Capitulum – flat receptacle with sessile flowers (e.g., sunflower).
5. What is a raceme in racemose inflorescence?
A raceme is a type of racemose inflorescence with an elongated main axis bearing pedicellate flowers in acropetal order. Its features include:
- Long, unbranched central axis.
- Each flower has a distinct pedicel.
- Older flowers at the base and younger at the top.
Common examples include mustard and radish.
6. What is the function of racemose inflorescence?
The function of racemose inflorescence is to enhance pollination efficiency and maximize seed production. It helps by:
- Producing a large number of flowers over time.
- Allowing sequential flowering due to acropetal arrangement.
- Increasing visibility to pollinators.
- Improving chances of cross-pollination.
This arrangement ensures better reproductive success in flowering plants.
7. What is acropetal succession in racemose inflorescence?
Acropetal succession is the arrangement in which older flowers are at the base and younger flowers develop towards the apex in a racemose inflorescence. This means:
- Flowering starts from the bottom.
- New buds continue to form at the top.
- The main axis keeps growing.
This pattern is a key identifying feature of racemose inflorescence.
8. Can you give examples of plants with racemose inflorescence?
Common examples of plants with racemose inflorescence include mustard, sunflower, banana, and coriander. Specific examples are:
- Mustard – raceme.
- Sunflower – capitulum.
- Banana – spadix.
- Coriander – umbel.
These examples represent different types of racemose inflorescence in flowering plants.
9. What is a spike in racemose inflorescence?
A spike is a type of racemose inflorescence in which sessile flowers are attached directly to an elongated main axis. Its main features are:
- Elongated, unbranched axis.
- Flowers lack pedicels (sessile).
- Acropetal arrangement of flowers.
Examples include Achyranthes and Plantago.
10. Why is racemose inflorescence called indeterminate?
Racemose inflorescence is called indeterminate because the main axis does not terminate in a flower and continues to grow. As a result:
- The apical bud remains active.
- New flowers keep forming towards the apex.
- The inflorescence can elongate over time.
This indeterminate growth pattern distinguishes it from determinate (cymose) inflorescence.
