The arrangement of flowers on the floaral axis (peduncle) is called inflorescence. It is basically of two types -Racemose and Cymose.

A. Racemose (Indefinite)

Main axis of inflorescence does not end in a flower but continues to grow.

The development of flowers is acropetal.

The opening of flowers is centripetal.

Concept Builder

Racemose inflorescence is of following types :

(i) Raceme. Peduncle has bisexual and pedicellate flowers arranged acropetally, e.g., Larkspur, radish.

(ii) Panicle. Peduncle branched and branches have pedicellate flowers, e.g. , Gulmohr, Rhus.

(iii) Spike. Peduncle has bisexual and sessile flowers, e.g. , Achyranthes, Adhathoda.

(iv) Spikelet. It is a small, special spike. Flowers are produced in the axil of fertile bracts called lemma, e.g., wheat, grasses (Poaceae).

(v) Catkin. It is pendulous spike in leaf axis which bears unisexual flowers, e.g., Morus, Birch, Oak, Acalypha.

(vi) Spadix. It is spike with fleshy axis and having both male and female flowers. It is surrounded by large coloured bracts called spathe, e.g., Musa, Palm, Colocasia, Alocasia (characteristically found in monocots).

(vii) Corymb. The main axis is short. Lower flowers have long pedicels than upper ones so that all the flowers are brought more or less to the same level, e.g., Iberis, Capsella.

Compound corymb, e.g., Cauliflower. Corymbose raceme is found in mustard.

(viii) Umbel. The main axis is reduced very much and all flowers appear to be arising from the same point. At the base of flowers, cluster of bracts form an involucre, e.g., Hydrocotyle. Scapigerous umbel is found in onion.

Compound umbel e.g., Coriander.

(ix) Capitulum or head. Main axis becomes flat and called receptacle. It bears many sessile and small florets. Peripheral florets called ray florets are pistillate or neuter and zygomorphic, whereas disc florets are bisexual and actinomorphic e.g., Sunflower, Zinnia, Cosmos (Asteraceae).

B. Cymose (Definite)

Main axis terminates in a flower. The development of flowers is basipetal and opening of flowers is centrifugal.

Concept Builder

Cymose inflorescence is of following types :

(i) Monochasial or uniparous cyme. A single lateral branch arises from a cymose axis which terminates in a flower. It is of two types:

(a) Helicoid cyme. When the lateral axis develop successively on the same side, forming a helix e.g., Atropa, Datura, Begonia, Heliotropium .

(b) Scorpioid cyme. Lateral branches (successive flowers) arise alternately on left and right sides (in zig zag manner), e.g., Ranunculus.

(ii) Dichasial or biparous cyme. Two lateral branches arise at a time from a cymose axis, which end into flower, e.g., Dianthus, Nyctanthes.

(iii) Polychasial or multiparous cyme. More than two lateral branches arise at a time from a cymose axis and all of them end into flowers, e.g., Hamelia, Calotropis.

(iv) Capitate. Large number of sessile flowers grow on a suppressed axis to form a globose structure. e.g., Acacia, Mimosa, Anthocephalus.

Special inflorescences : These are of following types :

(i) Verticillaster. A cluster of sessile or subsessile flowers borne on a dichasial cyme ending in monochasial cyme (scorploid) in the form of condensed whorl on either side of the node. e.g., Ocimum (Tulsi), Salvia (Lamiaceae).

(ii) Cyathium. It looks like a single flower. A cup shaped involucre formed by bracts encloses a single female flower and a number of male flowers. Each male flower is represented by single stamen, while a single pistil represents a female flower e.g., Poinsettia (Euphorbia pulcherrima), Pedilanthus .

(iii) Hypanthodium. Fleshy receptacle forming a hollow cavity with an apical opening called ostiole. The flowers are developed on inner wall of the hollow cavity. The male flowers are situated at the top near the opening, at the bottom are situated the female flowers with long styles and in between both are situated short styled gall flowers which are sterile. e.g., Ficus (Banyan, Fig, Gular).

(iv) Coenanthium. In Dorstenia, the receptacle becomes saucer shaped and its margins are slightly curved. The arrangement of florets is similar to hypanthodium.