Racemose Inflorescence - Types, Examples and Cymose

Racemose Inflorescence: In a flowering plant, a group of flowers on its branches is known as an inflorescence. There are various types of inflorescences based on how the flowers are arranged on a stem or its central axis, also known as the peduncle. Inflorescences are classified as either indeterminate or determinate based on this arrangement.

Sexual Reproduction in Flowering Plants

Racemose Inflorescence Meaning

• The main axis, called a peduncle, exhibits indefinite growth and continuously produces flower buds.
• Peduncles follow a monopodial growth pattern.
• Flowers are typically not grouped together closely.
• Flowers are arranged in acropetal succession, with older flowers located towards the base of the inflorescence and younger ones towards the apex.
• Flowers do not provide protective cover to newly formed fruits.
• A flower may not always be located at the tip of the peduncle.

Free Study Material for NEET Preparation

Racemose Inflorescence Types

1. Elongated Main-Axis

• Raceme: Simple inflorescence with flowers on short stalks of equal length at equal distances along an elongated axis, opening in succession toward the apex. Examples include mustard (Brassica campestris) and radish (Raphanus sativus).
• Compound Raceme or Panicle: Main axis is branched, with lateral branches bearing flowers in a simple raceme manner. Examples include Mango (Mangifera indica), Azadirachta indica (neem), etc.
• Spike: Main axis remains elongated, with lower flowers opening earlier than upper ones. Flowers are sessile. Examples include Amaranth (Amaranthus spp.), latjira (Achyranthes Aspera), etc.
• Spike of Spikelets: Compound spike with sessile flowers (spikelets) on branched main axis. Examples include Wheat, barley, sorghum, oats, etc.

2. Spikelets: Each spikelet can have one or more flowers (florets) attached to a central stalk called a rachilla. Arranged in a spike inflorescence, spikelets can be raceme, panicle, spike, or compound spike.

• Raceme Spikelet: Spikelets on pedicels attached to the rachis (central axis). Examples include Festuca, Paspalum (crown grass), Echinochloa (barnyard grass), etc.
• Panicle Spikelet: Spikelets attached to panicle branches. Examples include Avena, switchgrass, reed canary grass, Alopecurus (foxtails), etc.
• Sessile Spikelet: Attached directly to the rachis or panicle branches and lacks a pedicel. Examples include Hordeum, ryegrass, Triticum aestivum (Wheat), etc.

3. Catkin: Drooping spike with unisexual sessile flowers arranged close together on the peduncle. Examples include Morus alba (mulberry), Betula (birches), Salix (willows), etc.
4. Spadix: Formed when a spathe covers a spike. Found in monocotyledonous plants like Araceae, Musaceae, and Palmaceae. Compound spadix has branched main axis, with each branch bearing sessile flowers. Examples include coconut.
5. Shortened Main Axis

• Corymb: Flowers at the same level, with lower flower's pedicels longer than upper flower's. Branched main axis with flowers arranged like an umbrella. Examples include Hawthorn.
• Umbel: Main axis shortened, with flowers emerging from the axil of bracts. Can be simple or compound, with branches forming an "umbel of umbels." Examples include Centella Asiatica (Brahmi), Allium cepa (onion), Fatsia japonica (paper plant), etc.

6. Flattened Main Axis

• Capitulum: Main axis is suppressed and flat, allowing sessile flowers to form crowded patterns on the flat surface of the receptacle. Outer flowers are older and open earlier than inner ones.

Racemose Inflorescence Examples

1. Grapes ( Vitis vinifera) : The grapevine features a compound raceme, also known as a panicle. Each grape cluster forms a dense, branched structure with individual grapes attached to secondary axes.
2. Snapdragons ( Antirrhinum majus ): Snapdragons exhibit tall, slender racemes where flowers are arranged along the main axis. The flowers typically bloom from the base of the raceme upwards.
3. Orchids (Orchidaceae): Orchids display different types of racemose inflorescences, including the simple raceme, where flowers are directly attached to the main axis. The arrangement of flowers along the axis varies significantly among orchid species.
4. Sweet Pea ( Lathyrus odoratus ): Sweet peas showcase a type of raceme known as a simple raceme, where flowers are borne along the main axis. Compared to snapdragons, the raceme of sweet peas is usually longer, with flowers that open sequentially from the base to the tip.
5. Amaranth ( Amaranthus spp. ): Amaranth plants produce racemose inflorescences called spikes. These spikes feature densely packed flowers along an elongated, unbranched axis.

Explore - NEET Online Courses by PW

Racemose Inflorescence Acropetal

1. Indefinite growth of the primary axis: The peduncle continues to elongate during the flowering period, facilitating the development of new flowers at its tip.
2. Lateral flower bearing: Flowers are attached to the sides of the peduncle rather than at its terminal end.
3. Acropetal progression: Younger flowers are situated nearer to the tip, while older flowers are positioned towards the base of the stem.
4. Presence of stalked or sessile flowers: Individual flowers may possess small stalks (pedicels) attaching them to the primary axis, or they may be directly attached without a stalk.

Racemose Inflorescence And Cymose Inflorescence