what is inflorescence?
Flowers may occur singly, in groups, or in clusters. The arrangement axis is termed an inflorescence. An inflorescence is actually a closely branching in most plants the flowers are borne in groups but in some, they occur singly and are called Solitary. The solitary flower may be Terminal, when it is borne at the tip’ of the main stern or of its branch as in Poppy, or Axillary, when it is situated in the axil of a leaf, as in Garden Nasturtium.
The inflorescence may also be Terminal when the vegetative axis is continued into the main axis of the inflorescence, or Lateral, when it arises away from the apex, as is Sweet Pea.
It may be branched or unbranched. The main axis of the inflorescence is called Peduncle.
The inflorescence may be Simple, Compound, Mixed, or Of Special Types.
When branching of the main axis or peduncle is either racemose or cymose, the inflorescence is known as Simple. The simple inflorescence is of two types according to its mode of branching.
- Racemose Inflorescence: In this type of inflorescence the axis continues its growth until the last e flower is formed at its apex. The flowers are developed In acropetal Succession, i.e., the oldest flowers are towards the base of the inflorescence and the youngest ones towards the apex.
The main axis of a racemose inflorescence is sometimes may be compressed and flattened into a disc, bearing a cluster of flowers on its upper surface. In such cases, the arrangement of flowers is Centripetal, i.e., the oldest flowers towards the periphery and the youngest ones towards the Centre.
- Cymose Inflorescence: In this type of inflorescence, the main axis soon ends Flower. One, two, or more lateral branches develop below the terminal flowers, each ending in a flower and producing daughter axes. The flowers develop in Basipetal Succession, i.e., the terminal flower is the oldest and the lateral ones are younger.
In a cymose inflorescence, the flowers usually form Clusters. There is an arrangement of flowers in them is centrifugal i.e., the young flowers are towards the periphery and the older ones towards the center.
The main axis may be elongated, shortened, or flattened into a Therefore the classification of Racemose Inflorescence is based on the Development of the main axis and pedicels of the flowers.
Main Axis Long
- Simple Raceme: Main axis elongated. Flowers pedicellate. The pedicels of flowers are of the size, e.g., in Larkspur.
- Corymb: The main axis comparatively short. Flowers pedicellate. The pedicels of older flowers are longer than those of younger ones, so that all flowers lie at the same level, as in fibers (candytuft).
- Corymbose Raceme: Inflorescence corymbose in the flowering Stage but later on Becomes a simple raceme due to elongation of axis e.g., in Brassica.
- Spike: The main axis elongated bearing sessile flowers, as in Verbena, Bottle-brash.
- Spikelet: These are small dry spikes having only one or a few sessile flowers surrounded by special bracts at the base called Glumes, e.g., in Grasses, Wheat, Oat, etc.
- Catkin: It is a Pendulous spike with a pendulous axis bearing unisexual flowers. As in mulberry, Poplar.
- Spadix: It is a branched or unbranched thick. Fleshy spike enclosed in one or bracts, called Spathe e.g., in banana, palm. It is found in monocots only.
Main Axis Short & Flattened
- Simple umbel: The main axis above the first flower is so much shortened that the internodes between the successive flowers become suppressed. All ‘the pediculate flowers arise From the tip of the main axis at one level and the older ones towards the periphery, as in cherry. This inflorescence is the characteristics of Umbelliferon.
- Capitulum: The main axis is reduced to a flat, concave, or convex disc, the Receptacle.
The flowers are small and are known as Florets. The florets are crowded on the upper surface of the receptacle and while the inflorescence looks like a single flower. The young flowers are present in the center of the receptacle while the older ones toward the periphery. The receptacle is surrounded at the base by overlapping bracts which form an Involucre.
The capitulum may be homogamous, if all flowers are of the same kind, as in Sonchus, in which the flowers are ligulate (strap-shaped) and bisexual, or heterogamous, in which the flowers are of two types, as in sunflower, the Disc-Florets, tubular and bisexual, occupying the center of the receptacle and the ray florets, ligulate and pistillate or neuter, present at the periphery of the receptacle.
This type of inflorescence is characteristic of the composite.
- hypanthium: the receptacle grows upwards along its margins and forms a hollow, pear-shaped structure, which an apical opening guarded by scales. Unisexual flowers develop on the inner surface of the hollow receptacle. The male flowers are present near the apex while the female flowers occupy the rest of the surface, e.g., Banyan, Pepal.
Cymose Inflorescence may be Uniparous, Biparous, or Multiparous.
- Uniparous Cyme: The main axis ends in a flower below which a daughter axis is produced which again ends in a flower. The process is repeated many times. Uniparous cyme is of two types:
(a) Scorpioid cyme: successive daughter axes develop on right and left alternately, forming a zigzag, as in Freesia.
(b) Helicoid Cyme: Successive daughter axes are developed on the same side, either right or left, forming a spiral, e.g., in Begonia and some Solanaceae. In both cases, the basal portions of the successive daughter axes become straightened up, to form a false central axis or Sympodium. It is also called Sympodial Cyme, therefore.
- Biparous Cyme: The main axis ends in a flower and produces two daughter axes. Which of the two daughter axes again ends in a flower and produces two daughter axes which continue branching in the same way. The biparous type usually passes into a uniparous cyme by the suppression of one of the two branches at each subsequent branching. The biparous cyme is found in Ipomea, Stellaria, etc.
- Multiparous Cyme: The main axis ends in a flower and produces a whorl of three or more daughter axes, each of which continues to branch in the same manner, e.g., in Euphorbia.
The flowers are arranged in groups or clusters, each of which is really a scorpioid cyme in which the main axis and the successive daughter axes have been reduced and the flowers are almost sessile. The young flowers are either towards the periphery or scattered among the older flowers, as in Acacia, Albizzia.
If the main axis of the inflorescence is branched and the branches bear flowers in the same manner as are present on the main axis, the inflorescence is called a compound Inflorescence. Various types of compound inflorescences met within angiosperms are:
- Compound Raceme: A compound raceme consists of several simple racemes borne in a racemose fashion on the main axis, as in Delphinium.
- Compound Spike: The main axis of the inflorescence bears small lateral spikes instead of sessile flowers, e.g., in wheat, Barley.
- Compound Umbel: A number of umbels borne in an umbellate manner on the tip of the main axis. Bracts may or may not be present. If present at the base of the primary umbel. They are known as Involucre as in Coriander, Carrot.
- Compound Corymb: The main axis is branched in a corymbose manner and each branch is a simple corymb, as in Cauliflower (Phool Gobi).
- Compound Capitulum: Secondary capitulum consists of a single flower surrounded by an involucre (bracts present at the base of the flower) e.g., in echinus, veronica.
In some inflorescences, the daughter axes are extremely reduced and are crowded in many groups. It is difficult to make out the real mode Of branching in them. Therefore, these are termed special inflorescences.
In this, the axes are extremely reduced and the perianth leaves are completely suppressed. The main axis ends in a reduced female flower which is tricarpellary and syncarpous pistil, borne on a long stalk.
The flower is surrounded at its base by an involucre. Inside the involucre, surrounding the stalk.
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