Cymose and Racemose — Revision Notes

⚡ 30-Second Revision

Inflorescence — Arrangement of flowers on floral axis.
Racemose — Indeterminate growth, main axis continues. Flowers lateral.

- Succession: Acropetal (youngest at apex, oldest at base). - Opening: Centripetal (base to apex/periphery to center). - Types: Raceme (Mustard), Spike (Achyranthes), Spadix (Maize), Catkin (Mulberry), Corymb (Candytuft), Umbel (Coriander), Capitulum (Sunflower).

Cymose — Determinate growth, main axis terminates in a flower.

- Succession: Basipetal (oldest at apex, youngest at base). - Opening: Centrifugal (apex to base/center to periphery). - Types: Monochasial (Helicoid - Heliotropium; Scorpioid - Cotton), Dichasial (Jasmine, Dianthus), Polychasial (Calotropis).

2-Minute Revision

Inflorescence, the arrangement of flowers on a floral axis, is broadly classified into Racemose and Cymose types. The key differentiator is the growth pattern of the main axis. Racemose inflorescences exhibit indeterminate growth; the main axis continues to elongate, never terminating in a flower.

Flowers are borne laterally in an acropetal succession, meaning younger flowers are at the apex and older ones at the base. Flower opening is typically centripetal. Examples include the simple raceme (Mustard), spike (Achyranthes), specialized spadix (Maize), catkin (Mulberry), flat-topped corymb (Candytuft), umbel (Coriander), and capitulum (Sunflower).

Conversely, Cymose inflorescences show determinate growth; the main axis terminates in a flower, arresting its further elongation. Subsequent flowers arise from lateral buds below the terminal one, leading to a basipetal succession (oldest at apex, youngest at base).

Flower opening is usually centrifugal. Cymose types are further divided based on branching: Monochasial cyme (one lateral branch, e.g., Helicoid in Heliotropium, Scorpioid in Cotton), Dichasial cyme (two lateral branches, e.

g., Jasmine), and Polychasial cyme (more than two lateral branches, e.g., Calotropis). Mastering these distinctions and their examples is crucial for NEET.

5-Minute Revision

To revise Cymose and Racemose inflorescences for NEET, focus on the core differentiating features and specific plant examples. An inflorescence is simply the arrangement of flowers on the floral axis. The two major types are Racemose and Cymose.

Racemose Inflorescence (Indeterminate Growth):

Main Axis — Continues to grow indefinitely; its apical bud does not form a flower.
Flower Arrangement — Flowers are produced laterally along the elongating axis.
Succession — Acropetal – youngest flowers are at the apex (tip), and the oldest are at the base. This is like building a tower from the ground up.
Opening — Centripetal – flowers open from the base towards the apex (in elongated types) or from the periphery towards the center (in flat-topped types).
Key Examples & Types

* Raceme: Pedicellate flowers on an elongated axis. E.g., Mustard, Radish. * Spike: Sessile flowers on an elongated axis. E.g., Achyranthes, Amaranthus. * Spadix: Fleshy spike enclosed by a spathe.

E.g., Maize, Colocasia. * Catkin: Pendulous spike, usually unisexual. E.g., Mulberry. * Corymb: Lower flowers have longer pedicels, bringing all to the same level. E.g., Candytuft. * Umbel: All pedicellate flowers arise from a single point.

E.g., Coriander, Carrot. * Capitulum (Head): Sessile florets on a flattened receptacle. E.g., Sunflower, Marigold.

Cymose Inflorescence (Determinate Growth):

Main Axis — Terminates in a flower, arresting its growth.
Flower Arrangement — Subsequent flowers develop from lateral buds below the terminal flower.
Succession — Basipetal – oldest flower is at the apex, and younger ones are at the base. This is like a 'top-down' development.
Opening — Centrifugal – flowers open from the apex towards the base (in elongated types) or from the center towards the periphery (in flat-topped types).
Key Examples & Types

* Monochasial Cyme (Uniparous): One lateral branch below the terminal flower. * Helicoid: Branches on the same side, forming a coil. E.g., Heliotropium, Hamelia. * Scorpioid: Branches alternately on opposite sides, forming a zigzag.

E.g., Cotton, Begonia. * Dichasial Cyme (Biparous): Two lateral branches below the terminal flower. E.g., Jasmine, Dianthus, Bougainvillea. * Polychasial Cyme (Multiparous): More than two lateral branches below the terminal flower.

E.g., Calotropis, Euphorbia.

Quick Check: If the main stem keeps growing, it's Racemose. If the main stem stops growing because a flower forms at its tip, it's Cymose. Remember the succession and opening patterns associated with each. Practice identifying examples to solidify your understanding.

Prelims Revision Notes

Racemose Inflorescence (Indeterminate)

Main Axis Growth — Indeterminate; continues to grow, apical bud remains vegetative.
Flower Position — Lateral on the main axis.
Flower Succession — Acropetal (youngest at apex, oldest at base).
Flower Opening — Centripetal (base to apex or periphery to center).
Types & Examples (Crucial for NEET)

* Raceme: Pedicellate flowers on elongated axis. Ex: Mustard, Radish, Gulmohar. * Spike: Sessile flowers on elongated axis. Ex: Achyranthes, Amaranthus, Tuberose. * Spadix: Fleshy spike, enclosed by spathe.

Ex: Maize, Colocasia, Banana. * Catkin: Pendulous spike, usually unisexual. Ex: Mulberry, Oak. * Corymb: Lower flowers with longer pedicels, all reach same level. Ex: Candytuft, Cauliflower.

* Umbel: All pedicellate flowers from single point at apex. Ex: Coriander, Cumin, Carrot. * Capitulum (Head): Sessile florets on flattened receptacle. Ex: Sunflower, Marigold, Daisy.

Cymose Inflorescence (Determinate)

Main Axis Growth — Determinate; terminates in a flower, arresting growth.
Flower Position — Terminal on main axis, subsequent flowers from lateral buds below.
Flower Succession — Basipetal (oldest at apex, youngest at base).
Flower Opening — Centrifugal (apex to base or center to periphery).
Types & Examples (Crucial for NEET)

* Monochasial Cyme (Uniparous): One lateral branch below terminal flower. * Helicoid: Branches on same side, coiled. Ex: Heliotropium, Hamelia, Drosera. * Scorpioid: Branches alternately on opposite sides, zigzag. Ex: Cotton, Begonia, Freesia. * Dichasial Cyme (Biparous): Two lateral branches below terminal flower. Ex: Jasmine, Dianthus, Bougainvillea. * Polychasial Cyme (Multiparous): More than two lateral branches below terminal flower. Ex: Calotropis, Euphorbia.

Key Distinctions to Remember: Indeterminate vs. Determinate growth, Acropetal vs. Basipetal succession, Centripetal vs. Centrifugal opening. Focus on memorizing the classic examples for each sub-type, as these are frequently tested in NEET.

Vyyuha Quick Recall

To remember the key differences between Racemose and Cymose:

Racemose Always Continues Elongating, Making Oldest Structures Early (at base).

Cymose Yields Main Oldest Structure Early (at apex), Stopping Elongation.

Racemose: Acropetal, Centripetal, Indeterminate.
Cymose: Basipetal, Centrifugal, Determinate.

(Think 'RAC-I' for Racemose and 'CYM-BD' for Cymose to link the first letters of key terms.)