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Chapter: 11th 12th standard bio Biotany Plant Tree higher secondary school

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Description of a flower

The following technical terms are used in connection with the description of flower.

Description of a flower
 
The following technical terms are used in connection with the description of flower.

1. Floral whorls

 
             Complete: When all the four whorls. (Calyx, Corolla, Androecium, and Gynoecium) are present in a flower, it is termed complete.
 
             Incomplete: When one or more whorls are absent the flower is described incomplete.
 
a. Monochlamydeous: Some flowers have only one accessory whorl and they are called Monochlamydeous.
 
b. Dichlamydeous: Normally flowers have two outer whorls which are usually differentiated into calyx and corolla. Such flowers are known as dichlamydeous.
 
c. Achlamydeous: There are a number plants, where the flowers have neither calyx nor corolla. Such flowers are described naked or achlamydeous.

2. Sex distribution

 
             Bisexual or Perfect: When both the essential whorls i.e., androecium and gynoecium are present in a flower, it is called bisexual or perfect.
 
             Unisexual or imperfect: A flower having only one of the essential whorls is called unisexual or imperfect. The unisexual flowers may be of two types.
 
             Staminate. Male flower with androecium, only
 
             Pistillate. Female flower with gynoecium only
 
Monoecious
 
If male and female flowers develop in the same plant, it is called Monoecious eg. Coconut, Maize etc.
 
Dioecious
 
If male and female flowers are borne on separate plants, it is termed dioecious eg. Palmyrah palm, Papaya, Mulberry etc.

Polygamous
 
If a plant develops three kinds of flowers i.e. staminate, pistillate and bisexual flowers, it is called polygamous. eg. Mango, Cashewnut etc.
 

3. Floral Symmetry

 
The shape, size and arrangement of floral appendages (i.e. Calyx, corolla, androecium and gynoecium) around the axis of a flower is called floral symmetry. The axis to which the flower is attached is called mother axis. The side of flower towards mother axis is called posterior side and the side away from it is called anterior side.
 
On the basis of floral symmetry there may be following three conditions of a flower.
 
    Actinomorphic: A flower with radial symmetry, i.e., the parts of each whorl are similar in size and shape. The flower can be divided into two equal halves along more than one median longitudinal plane, eg. Hibiscus, Solanum, etc.
 
    Zygomorphic: A flower with bilateral symmetry, i.e. the parts of one or more whorls are dissimilar. The flower can be divided into two equal halves in only one vertical plane, eg. Pisum
              Asymmetric: A flower which cannot be divided into two equal halves along any vertical plane, eg. Canna
 

Arrangement of floral organs

 
              Cyclic: The floral parts are arranged in definite whorls around the axis of flower, eg. Brassica, Solanum etc.
 
              Acyclic: The floral parts are arranged in spirals and not in whorls, eg. Magnolia
 
              Spirocyclic: Some of the floral parts are in whorls and others in spirals (Hemicyclic), eg. Rose, Ranunculus, etc.
 

Number of floral parts

 
Occurrence of the same number of floral parts in different floral whorls of a flower is called isomery. Sometimes, flowers have different number of parts in each whorl. This condition is called heteromerous. The isomerous flowers may be of the following types:-
i. Dimerous    Floral parts in two's or multiplies of two
ii. Trimerous  Floral parts in three's or multiples of three
iii. Tetramerous       Floral parts in four's or multiples of four
iv.Pentamerous        Floral parts in five's or multiples of five
 

Dicotyledonous flowers are usually tetra, or pentamerous whereas monocotyledonous flowers are trimerous or multiples of three.


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