Inflorescence and its types

• The arrangement and distribution of flowers over a plant is called inflorescence.
• The axis of inflorescence is called peduncle.
• A flattened peduncle is known as receptacle.
• It is of five types: solitary, racemose, cymose, mixed and specialized.

Types of inflorescence

1) Solitary

• Flowers occur singly or separate from other flowers.
• It is of two types:

a) Solitary terminal: single flower occurs at the tips. e.g., Papaver.

b) Solitary axillary: single flower occurs in the axial. e.g.,China rose.

2) Racemose

• It is indefinite or indeterminate type.
• Arrangement of flowers is accropetal succession (older towards base and younger towards tips).
• It is of two types:

a) Simple racemose:

• Peduncle is unbranched.
• It is of various types. They are as follows:

i) Typical raceme:

• Peduncle bear stalked or pedicellate flowers.
•  e.g., Delphinium, Radish.

ii) Corymb :

• Pedicle of lower flowers is longer.
• In this way, all the flowers lie at the same level.
• e.g., Candytuft (Iberis).

iii) Corymbose raceme:

• e.g. Mustard.

iv) Umbel:

• All the flowers arise from the single point.
• e.g., Centella, Androceae, etc.

v) Spike:

• Sessile flowers at accropetal succession.
• e.g., bottle brush (Callistemon), Chaff flowers (Achyranths), Adhatoda.

vi) Catkin:

• It is unisexual spike.
• e.g., Mulberry (Molus), Willow (Salix), Betula (Birch)

vii) Spadix:

• It is fleshy spike partially covered by leafy bract called spathe.
• e.g., Colocassia, Arisaema (snake or cobra plant).

viii) Capitulum or racemose head:

• The peduncle is flattened to form a receptacle that bear small sessile flowers called florets.
• The florets are arranged in centripetal fashion.
• The inflorescence is surrounded by one or more whorls of bracts called involucre.
• e.g., found in many compositae flowers like Tagetes, Zinnia, Helianthus annuus (sunflower), Chrysanthemum, etc.

Image source: examplespedia

b) Compound racemose

i) Panicle:

• Compound raceme.e.g., Cassia fistula, Asphodelus, Yucca, Neem, (Azadirachta indica).

ii) Spikelets:

• Spike of spikes e.g., Amaranthus.

3) Cymose

• It is definite or determinate inflorescence.
• The arrangement of flower is basipetal (older flowers lie at the top and younger at the bottom).
• It is of three types:

i)Uniparous or Monochasial Cyme:

• The terminal bud of main axis ends in a flower.
• A single lateral branch pushes it to one side, which also terminates into a flower.
• It is of two types:

a. Helicoid:

• All the flowers are borne on the same side forming a sort of helix.
• e.g., Drosera, Begonia, Heliotropium, etc.

b. Scorpioid cyme:

• Flowers are alternately borne on both the sides.
• e.g., Freesia, Ranunculus, etc.

ii) Biparous or Dichasial Cyme:

• A terminal flower is subtended by two lateral branches, which also ends in a flower.
• e.g., Silene, Jasmine, Clerodendron, Bougainvillea, etc.

iii) Multichasial or Polychasial Cyme:

• Numerous flowers are produced on the lateral sides.
• e.g., Calotropis, etc.

4) Special inflorescence

• It is also of various types.
• They are as follows:

i) Cyathium:

• It looks like a single flower.
• In the centre, there is a single female flower represented by gynoecium only which is surrounded by many male flowers.
• All flowers are enclosed by involucre of bracts.
• e.g., Euphorbiaceae.

ii) Verticellastar:

• It is a condensed form of cymose.
• In the axil of opposite leaves dichasial cymes are found in cluster and appears like whorls called verticellaster.
• e.g., Salvia, Ocimum, etc.

iii) Hypanthodium:

• Inflorescence axis becomes fleshy and pear shaped with a hollow cavity inside.
• Female flowers at the base and male flower towards apical opening.
• e.g., Ficus.

5) Mixed inflorescence

i) Thyrsus

• A mixture of raceme and cyme.
• Main axis shows racemose while the lateral axis shows cymose inflorescence.
• e.g., Lilacs, grape vine.

References: 

i) http://hsvbg.org/wp-content/uploads/2016/06/Types-of-Inflorescence_N-Ontario-Plant-Database.pdf

ii) https://collegedunia.com/exams/inflorescence-definition-types-and-examples-biology-articleid-1595

Inflorescence and its types