Inflorescence | Definition, Classification and Types of Inflorescence
The shoot modifies to form the flower i.e., the flower is considered as the modified shoot. When the apical shoot meristem changes to floral meristem then the shoot bears flowers. During the formation of floral meristem the axis condenses and internodes do not elongate. The axis bears flowers at successive nodes instead of leaves.
The flowers are borne either singly or in clusters on the shoot. When the shoot tip transforms into a flower, it is always solitary. The arrangement of flowers on the floral axis of the plant is known as inflorescence.
The flowers can be arranged in different ways, depending upon whether the shoot apex continuous to grow or convert into a flower. Two major type of inflorescence that can occur are:
(i) Racemose: In racemose inflorescence, the shoot axis continue to grow indefinitely and the flowers are borne in an aCropetal succession i.e., younger flowers are present towards the apex and the older flowers are present at the base e.g., radish, lupin, mustard.
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| Racemose inflorescence is of following types :
(a) Raceme : Peduncle has bisexual and pedicellate flowers arranged acropetally, e.g. Larkspur, radish. (b) Panicle. Peduncle branched and branches have pedicellate flowers, e.g., Gulmohur, Rhus. (c) Spike. Peduncle has bisexual and sessile flowers, e.g., Achyranthes, Adhath oda. (d) Spikelet. It is a small, special spike. Flowers are produced in the axil of fertile bracts called lemma, e.g., wheat, grasses (Poaceae). (e) Catkin. It is pendulous spike in leafaxis which bears unisexual flowers, e.g., Morus, Birch, Oak, Acalypha. (f) Spadix. It is spike with fleshy axís 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). (g) Corymb. The main axis is short. Lower flowers have long pedicels than upper ones so that all 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. (h) 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 bracis form an involucre, e.g., Hydrocotyle. Scapigerous umbel is found in onion. Compound umbel e.g., Coriander. (i) 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). |
(ii) Cymose: In cymose inflorescence, the main axis (peduncle) terminates into a flower and hence has a limited growth. In cymose inflorescence the flowers are borne in a basipetal order. e.g., Begonia, Teak, Bougainvillea, Dianthus, Solanum.
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| Special inflorescences : These are of following types :
(a) Verticillaster. A cluster of sessile or subsessile flowers borne on a dichasial cyme ending in monochasial cyme (scorpioid) in the form of condensed whorl on either side of the node. e.g. Ocimum (Tulsi), Salvia (Lamiaceae). (b) 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., Poinsetia (Euphorbia pulcherima), Pedila nthus. (c) Hypanthodium. Fleshy receptacle forming a hollw 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). |