Racemose Inflorescence

A racemose inflorescence is a type of indeterminate inflorescence where the main axis continues to grow, producing flowers along its length. It is characterized by a central axis that doesn't terminate in a flower but continues to elongate, producing flowers at the nodes. Flowers are borne laterally in an acropetal order/acropetal succession (Where old flowers are arranged at lower side and young flowers are at upper side).

1.0Key Features of Racemose Inflorescence

1. Main Axis Growth: The primary axis, or main stem, continues to grow without terminating in a flower or bud.
2. Flowers Arrangement: Flowers are attached to the main axis at the nodes, typically singly or in groups. The arrangement is acropetal, meaning that the younger flowers are towards the apex.
3. Indeterminate Growth: Racemose inflorescences exhibit indeterminate growth because the main axis doesn't end in a flower. This allows for continuous growth and the production of additional flowers.

2.0Types of Racemose Inflorescence

Racemose plant inflorescence is further divided into different types on the basis of growth of the main axis. These are as follows : 

1. Raceme - In this type of inflorescence, the peduncle (main axis or floral axis) is elongated and flowers are pedicellate. e.g. Radish, mustard (Brassicaceae). 

• Compound raceme - When the peduncle is branched and each branch bears pedicellate flowers like raceme and are arranged in acropetal manner then it is known as compound raceme or Raceme of racemes or panicle e.g. Gulmohar, Cassia.

2. Spike - In this type of inflorescence peduncle is elongated but flowers are sessile (without pedicel). e.g. Achyranthes.

• Spike of Spikelets - When the peduncle is branched and each branch bears a spike like inflorescence then the small branch having flowers is called spikelet and this arrangement is called spike of spikelets. e.g. Grass family (Gramineae = Poaceae).

3. Catkin/Amentum - In this type of inflorescence peduncle is thin, long and weak, and flowers are sessile and unisexual unisexual flowers develop on separate catkins. e.g. Mulberry (Shahtoot).

4. Spadix - In this type of inflorescence peduncle is thick, long and fleshy and it has small sessile and unisexual flowers covered with one or more large green or colorful bracts (spathe). e.g. Colocasia, maize, aroids. (palms - compound spadix). 

5. Corymb - In this type of inflorescence peduncle is short and all flowers are present at the same level because the lower flower has much longer pedicel than the upper ones. e.g. Candytuft (Iberis amara) = chandani, Capsella.

• Compound corymb -

If the peduncle is branched and each branch has a flower cluster, then this type of inflorescence is called compound corymb or corymb of corymbs. eg. Cauliflower. 

6. Umbel - An inflorescence in which the flower stalks (Pedicels) are of more or less equal in length, arise from the same point. At the base of the flower stalk, there is a whorl of bracts forming the involucre. e.g. Centella (brahmi)

• Compound umbel - If peduncle is branched and each branch has flower cluster then this type of inflorescence is called compound umbel or umbel of umbels e.g. Coriandrum (coriander or dhania), Foeniculum (fennel or saunf), Cuminum (cumin or jeera) (Umbelliferae or Apiaceae family).

7. Capitulum/Racemose head (Anthodium)

• In this type of inflorescence the tip of the peduncle becomes broad, flattened concave or convex (receptacle). On it small sessile flowers are found. These flowers are called florets. 
• The florets which are present in the centre are small & called disc florets and florets which are present at the periphery are large & called ray florets, florets are arranged in centripetal order. 
• In this type of inflorescence florets may be unisexual, bisexual and sterile. This inflorescence is surrounded by one or more involucre. 
• It is the most advanced type of inflorescence, because a single insect can easily pollinate innumerable florets within a very short time without having to fly from one flower to another. The ultimate advantage is that this mass pollination helps the setting of seeds in most heads for reproduction, multiplication in number and continuity of species. e.g. Compositae/Asteraceae family [Sunflower, zinnia, marigold (Tagetes)].

Also Read Corolla of a Flower and Morphology of Flowering Plants