MORPHOLOGY OF ANGIOSPERMS: INFLORESCENCE

· The arrangement of flowers on a floral axis is called an inflorescence.
· Anthotaxy refers to the arrangement of flowers in an inflorescence.
· The axis of the inflorescence is called a peduncle.

· A flattened peduncle is known as a receptacle

Broadly Inflorescence is two types:
i. Racemose Infloresence
· Terminal bud grows indefinitely giving flowers laterally so that younger flowers are at the tip and older are at the bottom.
· Acropetal succession (older flower toward base younger towards the tip)
· Order of opening of flowers is centripetal.
ii. Cymose Inflorescence
· Terminal bud ends in a flower with lateral buds giving rise to a younger flower.
· Older flowers are present at the top and younger flowers are at the bottom.
· Flowers are in basipetal succession (older flower – at the top, younger at the base)
· Order of opening of flowers is centrifugal.

A. Racemose type
a. Main Axis elongated
i. Raceme – The main axis is elongated and bears flowers i.e. Pedicellate flowers in an acropetal manner. e.g. Delphinium
ii. Spike – It is a raceme but the flowers are sessile i.e. without stalks. e.g. Adhatuda, Achyranthus (chaff flowers)
iii. Catkin – It is like a spike but differs in having a long pendulous axis. Generally with unisexual flowers. e.g. Mulberry.
iv. Spadix – It is a spike with a fleshy axis enclosed by one or more bracts called spathes. e.g. Neuter, male and female unisexual flowers are surrounded by a large bract called the spathe. e.g Arisaema, (snake/cobra plant)

Fig: Main axis elongated Racemose

B. Main Axis Shortened.
a. Corymb: Pedicel of a lower flower is longer but the pedicel of the upper flower is comparatively shorter so that all the flowers lie at the same level. e.g. Candytuft (Iberis)
· The stalk of the individual flower is called a pedicel.
· The main axis of the inflorescence together with the lateral axis if present is known as the peduncle.
b. Corymboraceme – a mixture of raceme + corymb eg. mustard
c. Umbel – The flower stalk is of equal length and arises from the same point. e.g. Centella, Androceae.
d. Compound umbel – Pedicel is branched in umbel manner. Each ray bears pedicellate flowers in an umbel manner. e.g. Coriander.

C. Main Axis Flattened
Head or capitulum
· The peduncle is suppressed, becoming almost flat and it bears masses of small sessile flowers (florets) on its surface, with one or more whorls of bracts at the base forming an involucre. These florets are common of two types
· Ray florets – Marginal, strap-shaped
· Disc florets – Central, tubular one.
· A Head or Capitulum is the characteristic of the sunflower family. e.g. Sunflower, marigold, cosmos etc.

B. Compound Raceme or Panicle
The peduncle is branched in an acropetal and racemes are born acropetally on each branch of the peduncle.
e.g. Male flower of maize, Gulmohar (Delonix regia), Casia, fistula, Yucca, Neem (Azadirachta indica)

C. Cymose
· Flowers are arranged in basipetal (centrifugal) succession (old at top and young at base).
· Often called definite or determinate.
a. Uniparous or Monochasial cyme
· The main axis terminates in a flower and young branches come off from the parent stem.
· Each lateral branch ends in a flower.
Two types
i. Helicoid (One-sided) cyme
· When the lateral axes develop successively on the same side, eventually forming a sort of helix.
e.g. Begonia, Drosera (sundew), Day lily (Hemerocallis)
ii. Scorpioid
· Lateral branches develop on alternate sides, evidently forming a zigzag structure. e.g. Cotton, Crassula, Freesia, Ranunculus.

b. Dichasial cyme or Biparous cyme
· A cyme - where lateral branches develop on both the sides of the terminal flower.
· Each branch terminates in a flower and the pattern repeats.
e.g. Jasmine, Dianthus, Bougainvillaea (glory of the garden)

c. Multiparous or Polychasial cyme
· The main axis as usual ends in a flower and gives off a number of lateral branches, each terminating in a flower. e.g. Calotropis

Other Special types of Inflorescence
I. Cyathium
· It is a modified cyme that looks like a flower and is a characteristic of Euphorbia.
· Number of male flowers seated on short stalk surrounds a single female flower in the centre.
· Presence of a cup-shaped involucre often provided with nectar secreting glands.
· Flower follows centrifugal order of development i.e. female flower matures first then males. e.g. Euphorbia (LaluPate)

Fig: Cythium Inflorescence.

II. Hypanthodium
· When the fleshy receptacle forms a hollow cavity with an apical opening guarded by scales and the flowers are borne on the inner wall of the cavity.
· Female flowers develop at the base of the cavity and the male flowers higher up towards the apical pore.
· E.g. Ficus (peepal), Banyan, Fig
· Hypanthodium inflorescence is the characteristic of the Fig family.
· 3 types of flowers are found in Hypanthodium inflorescence.

III. Verticillaster
· A special type of cymose inflorescence.
· In the axil of opposite leaves dichasial cyme are found in clusters and appears like whorls called verticillasters.
· E.g. Ocimum
· It is the characteristic of family Labiatae.
· Dichasial cyme ends into monochasial cyme in verticillaster inflorescence

High Yeilding Points from INFLORESCENCE

1. Solitary terminal: Papaver somniferum, Poppy plant (@ STP)
Solitary axial: eg; China rose

2. Recemose type:
i. Typical raceme: pedicellate eg: Radish
ii. Spike: eg Adhatoda vasica, Callistemon (Bottlebrush) and Achyranthes (Chaff flower)
iii. Catkin or Amentum: eg Morus, Salix alba, Betula (@ MBA)
iv. Spadix: eg Colocasia, Arisaema (Cobra or snake plant) (@ SPACE) but compound spadix: Palm coconut, Banana (@PCB)
v. Umbel: Pedicle of equal length eg: Centella, onion, Compound umbel: Coriander
vi. Corymb: Pedicle of different lengths. eg: Candytuft Edible inflorescence of Brassica oleraceae ver Botyrytis

(Cauliflower is compound corymb)

3. Cymose inflorescence:
a. Monochasial:
i. Helocoid cyme or one-sided cyme: e.g.: Begonia, Drosera, Helicotropium (@ BDH)
ii. Scropoid cyme: Successive branches are produced on both sides. Eg: Ranunculaceae
Note: Rhiphidium is a modified scorpioid cyme. Here all the flowers are on only one plane.
b. Dichasila Cyme or biparous Cyme: The main axis terminate by giving rise to two lateral branches. Eg: Dianthus, jasmine, Bougivillea (@ DJ.BOSS)
c. Multiparous Cyme: Eg: Calotropis

The involucre is whorl bracts surrounding an inflorescence. Eg: Capitulum, Cythium, Umbel

4. Cauliflory or trunky flory: development of the flowers from dormant buds on old stem or the trunk. eg: Ficus, Atrocarpous (jack fruit)

5. Hypanthodium looks like fruit while Cyathium looks like a flower.

6. In the hypanthodium, the male flower is at apex, female at base and gall (sterile) in between.

Also, Read Notes of other Lesson of Botany:

• Morphology of Stem
• Morphology of Root
• Morphology of Leaf
• Morphology of Fruit
• Morphology of Flower
• Morphology of Inflorescence
• Morphology of Seed