Inflorescence

The mode of arrangement of flowers on a specialized branch on top of the plant which bears flowers is called inflorescence. The axis of the inflorescence is called peduncle.

1. Sometimes the flowers are borne singly, such arrangement is said to be Solitary.
2. When solitary flowers are borne at the tips of branches or main stem they are described as Solitary terminal. E.g. Poppy.
3. They may be borne in the axil of a foliage leaf and are termed as Solitary axillary e.g. Petunia.

Garden Nasturtium and Hibiscus rosa-sinensis (China rose)

Like branching inflorescence also may be recemose or cymose. It may also be mixed type when it is partly racemose and partly cymose.

1. Recemose or indefinite inflorescence

The peduncle grows indefinitely and bears flowers in acropetal order i.e. older ones at the base and younger flowers near the apex or growing point.

1. Flower stalked:

Raceme: When the pedicellate (stalked) flowers are borne acropetally on an elongated axis e.g. Raphanus Crotolaria.

2. Flower sessile

1. Spike: Inflorescence is similar to raceme but the flowers are sessile e.g. Achyranthes aspera, Callistemin (Bottle brush), Antirrhinum (Dog flower).
2. Catkin or Amentum: A catkin is a spike in which the axis is thin and weak. Flowers are sessile and borne in acropetal order as in spikes the catkin is mostly pendulous and flowers are unisexual.
3. Spadix: It is a modification of spike having thick and fleshy peduncle, which may be variously coloured on the upper side. e.g. Colocasia (Arum), Amorphophllus titanium, banana etc.
4. Spikelet: It is a type of very small spike with one or few florets. Spikalets are arranged in spite, raceme or panicle fashion. Each spikelet bears at its base two minute bracts called empty glumes. e.g. Wheat, rice, oat, bamboo, sugarcane.

3. Peduncle shortened

1. Corymb: In Corymb peduncle is shortened. Pedicellate flowers borne at different points reach at the same level.
2. Corymbose raceme: The young flowers appear to be arranged like corymb but in mature state the longer pedicels of the lower flowers do not bring them to the level of upper ones e.g. mustard.

4. Peduncle flattened to form receptacle:

Capitulum: This is the characteristic inflorescence of family compositae. The peduncle forms a flattened more or less convex receptacle, on which very small sessile flowers called florets are arranged in a centripetal order.

1. The florts present at the centre of receptacle are termed as disc florets.
2. While peripheral florets are known as ray florets.
3. The whole capitulum is surrounded by an involucre or Bracts.

2. Cymose or definite inflorescence

In this case the main stops its growth and terminates into a flower. The lateral branches appear below it, which also terminate into flowers.    

Characters	Spadix	Capitulum
1. Nature of peduncle   2. Bract	Peduncle is thick and fleshy. The flowers enclosed by the leafy bracts or spathe.	Peduncle is short and is in the form of receptacle. The bracts are at the base in the form of involucre.

 

 Verticillaster: In this case a cluster of sessile or almost sessile flowers appear in the axil of leaf forming a false whorl or vertical at the node.         

Comparison among hypanthodium, cyathium and verticillaster.

Character	Hypanthodium	Cyathium	Verticillaster
Definition and example	The main axis forms a cup-shaped receptacle with a small opening at the top. Flowers are enclosed within the cup in cymose groups (Ficus).	In this inflorescence the involucre forms a cup, single female flower (without perianth) arises in the middle surrounded by a large number of male flowers represented by stalked stamens (Poinsettia, Euphoribia).	In the inflorescence, typical of plants with opposite leaves, a cyme arises in each leaf axil. The first axis ends in a flower. The branches arise below it bearing branches in an alternating manner. Flowers are sessile and appear as a cluster (Ocimum) around the node.