Question

A flower which can be divided into two equal halves by only one plane is
(a)Zygomorphic
(b)Actinomorphic
(c)Regular
(d)Perfect

Answer 1

Hint: Floral symmetry is the phenomenon describing whether a flower can be divided into two or more identical parts, and if yes then in which or how many planes. When the flower can be divided into two equal halves in a single plane only, it is also called irregular.

Complete answer:
When a flower is divided into two mirror-image halves by a single plane only, it is called as bilaterally symmetrical. Such a type of flower is said to be zygomorphic. The term zygomorphic is derived from Greek terms “zygon” meaning “yoke” and “morph” meaning “shape”.
Some examples of zygomorphic flowers include orchids and most members of the family Lamiales. Sometimes, this type of symmetry can also be referred to as monosymmetry.

Additional Information: Another type of symmetry is the radial symmetry which is seen in the actinomorphic arrangement of flowers. It is the most common type of symmetry and is sometimes considered as a primitive trait as compared to the evolved bilateral symmetry.
Actinomorphic flowers have a radial symmetry or a regular symmetry, which means they can be divided into two mirror-image halves in more than one plane, or they can be divided into 3 or more identical sectors.
Actinomorphic flowers are seen in plants such as Oleander, flowers of the family Liliaceae, and many floral families.
So, the correct answer is, “Zygomorphic.”

Note: -Sometimes a few plant species may be lacking any symmetry at all too. This may be due to a spiral arrangement of the floral whorls. They are called asymmetrical flowers.
Such types of flowers are seen in plants such as Caleriana officinalis and Canna indica.
-In some cases such as daisies and dandelions, the flowers seem to be actinomorphic, but they are actually a compactly arranged radially symmetric inflorescence. The small individual flowers may or may not be actinomorphic.
Such an inflorescence is called a head or a capitulum.
-Sometimes, symmetry groups are mentioned. They indicate the rotational symmetry. For example, monocots usually are present as trimerous flowers, i.e., they have petals in the multiples of three and have rotational symmetry of the order 3.