What is Inflorescence?
The arrangement of solitary flower or a group of flowers on the specialized floral axis or peduncle is known as inflorescence or anthotaxy. An inflorescence is categorized on the basis of the arrangement of flowers on a main axis and by the timing of its flowering.
Description of Inflorescence
In the flowering plants (angiosperms) the flowers are the sexual reproductive organs and they develop from specialized floral buds remaining at the axils of leaves or at the apices of shoots. The axillary floral buds develop into solitary axillary flowers (e.g., chinarose), while the apical bud forms the solitary terminal flowers (e.g., Datura). But sometimes the flowers may remain in an aggregated condition and the arrangement of flowers on the floral stalk or peduncle is known as inflorescence.
Sometimes flowers directly come up from the peduncle or sometimes they are borne on minute stalks called pedicels. The growth of the peduncle may be indefinite, i.e., flowers arising in acropetal succession from base to apex and it is called racemose inflorescence. Sometimes the stalk of racemose inflorescence may grow beyond the flowers and it is called rachila, (e.g., grass). In some cases, the racemose stalk is secluded by spathy bracts and it is called spadix (e.g., Musa). Sometimes the inflorescence stalk may form a flattened, fleshy, expanded structure called receptacle and the flowers are arranged on it, it is called capitulum (e.g., sunflower). The inflorescence stalk of underground modified stem like the bulb of onion is a fat stem called scape.
The inflorescence usually emerge from the aerial shoot and it is termed as cauliflory or cladanthy (e.g., Jackfruit), it is of two types viz.,
(i) Inflorescence stalks directly emerging from trunk called trunciflory (e.g., papaw).
(ii) Inflorescence stalks arising from the aerial branches e.g., Ixora.
Sometimes the inflorescence stalks may be borne on the leaves or lamina and called epiphyllous inflorescence (e.g., Begonia).The inflorescence stalk may sometimes be delimited with a terminal flower and it is called cymose inflorescence (e.g., Heliotropium), in this case, the flowers appear in basipetal succession, i.e., the terminal flower is first matured followed by the lower flowers.
Structure of Inflorescence
i) The inflorescence may be represented by a single flower or a group of flowers.
ii) The inflorescence stalk is called peduncle or rachis and the stalks of individual flowers are called pedicels.
iii) There are two main types of inflorescences, viz., the determinate or cymose and the indeterminate or racemose.
iv) Sometimes the inflorescence may be mixed, that means, with both racemose and cymose characters.
v) There are also some special types of condensed cymose inflorescences.
vi) The rachis may be simple or un-branched, as in spike or branched or compound panicle.
vii) The rachis may be subtended by a basal bract-like structure and called bracteate (e.g., Adhatoda) or sometimes it may be without bract and called ebracteate; e.g., Amaranthus.
viii) Sometimes there may be bracteoles present at the base of individual flowers; e.g., lemma and palea of spikelet of rice.
ix) In some cases, the inflorescence are never exposed, rather they remain covered within the receptacle.
x) At times, the flowers may be without pedicel or sessile in nature.
Classification of Inflorescence
There are four major types of inflorescences, those are:
i) Racemose or indefinite
ii) Cymose or definite
iii) Mixed type
iv) Special cymose.