The arrangement of flowers on the floral axis or peduncle is termed as inflorescence.Depending on whether the apex gets developed into a flower or continues to grow, two major types
of inflorescences are defined – racemose and cymose.
01. Racemose :
Position of flower : Lateral
Growth of Peduncle : Unlimited (Indefinite)
Floral axis (Peduncle) doesn’t terminate in a flower
Arrangement of flowers : Acropetal (i.e., younger flower towards apex and older flower towards base of floral axis)
Position of flower : Terminal
Growth of Peduncle : Limited (definite)
Floral axis (Peduncle) terminates in a flower
Arrangement of flowers : Basipetal
In this type of inflorescence the main axis continues to grow and does not terminate in a flower and flowers are borne laterally in an acropetal order/acropetal succession. Types of racemose inflorescence :
(A) Raceme : In this type of inflorescence, peduncle (main axis or floral axis) is elongated and flowers are pedicellate. e.g. Radish, Mustard.
When peduncle or floral axis of raceme gets branched and produces pedicellate flowers in acropetal order, it is known as Panicle or branched /compound raceme.
e.g. Cassia, Gulmohar
(B) Spike : In this type of inflorescence peduncle is elongated but flowers are sessile (without pedicel).
e.g. Achyranthes
When peduncle is branched and each branch bears spike like infloresence then the small branch
having flowers is called spikelet and this arrangement is called spike of spikelets. e.g. Wheat (Member of family poaceae).
(C) Spadix : In this type of inflorescence peduncle is thick, long and fleshy and it has small sessile and unisexual flowers covered with one or more large green or colourful bracts (spathe). e.g. Maize Colocasia, Maize.
Compound spadix e.g. Palms Grain of maize is a fruit (caryopsis).
Long filamentous threads (Silky hairs) protruding at the end of a
young cob of maize are styles.
(D) Capitulum/Racemose head (Anthodium) : In this type of inflorescence tip of peduncle becomes broad, flattened concave or convex (receptacle). On it small sessile flowers are found. These flowers are called florets. The florets which are present in centre are small & called disc florets and florets which are present at periphery are large & called ray florets, florets are arranged in centripetal order. In this type of inflorescence florets may be unisexual, bisexual and sterile. This inflorescence is surrounded by one or more involucre. It is most advanced type of inflorescence, because a single insect can easily pollinate innumerable florets within a very short time without having to fly from one inflorescence to another. e.g. Compositae /Asteraceae family [Sunflower, marigold (Tagetes)].
2.Cymose : In this type of inflorescence, the main axis/peduncle Cymose inflorescence terminates in a flower hence is limited or definite in growth. Flowers are arranged in basipetal succession/basipetal order.
Types of cymose inflorescence :
a. Uniparous or Monochasial Cyme : In this type, the peduncle ends in a flower and from lower part of the peduncle each lateral branch forms a single flower in a basipetal order. e.g. Solanum, Atropa.
b. Biparous cyme / Dichasial cyme : In this type of inflorescence peduncle ends in a flower and from the basal part of peduncle two lateral branches arise which also end in a flower, now this same arrangement occurs on these lateral branches. e.g. Bougainvillea, jasmine.
3.Special Type of Inflorescence :
Hypanthodium :In this type of inflorescence upper part of peduncle is modified into a pear-shaped structure having cavity with a pore (ostiole). At the base of cavity female flowers develop while towards the pore male flowers develop. All three types of flowers (male, female, sterile female) are present in this inflorescence. e.g. Ficus species – banyan, fig, peepal.
