Flower:
The flower is the most important and conspicuous organ of an angiospermic plant.
It is defined as highly modified and condensed reproductive shoot, specially designed for sexual reproduction.
Parts of a typical flower:
A flower, like a vegetative shoot (branch) may develop in the axil of a small leaf called bract, such a flower is called bracteate flower.
A flower without bract is called ebracteate flower.
Flower is produced on a stalk called pedicel.
The flower with a stalk is called pedicellate or stalked flower while a stalk-less flower is called non-pedicellate or sessile flower.
The terminal end of the pedicel is swollen (or expanded) and represents floral axis, called thalamus.
In a typical flower thalamus consists of four compactly arranged nodes and three highly condensed internodes.
From each node of thalamus, a circle or whorl of modified leaves is produced.
A flower consists of four circles of modified leaves called floral whorls.
These are named as calyx, corolla, androecium and gynoecium.
The floral whorls are classified into following two groups;
1. Accessory whorls: These are outer two whorls, calyx, (sepals) and corolla (petals) which do not take direct part in sexual reproduction.
2. Essential whorls: These are inner two whorls, androecium (stamens) and gynoecium (carpels) which take direct part in sexual reproduction.
A flower having all the four floral whorls is called complete flower.
The absence of any one or more floral whorls makes the flower incomplete.
A flower having both the essential whorls is called perfect or bisexual or hermaphrodite flower.
If a flower contains only one of the two essential floral whorls, it is called imperfect or unisexual-flower
A unisexual flower may be
male or staminate flower (if only stamens are present)
female or pistillate flower (if only carpels are present).
When both the essential whorls are absent, the flower is said to be neuter.
Monoecious plants
The plants which bear both the types of unisexual flowers (staminate and pistillate) are called monoecious plants,
e.g. maize, Cucurbita, etc.
Dioecious plant
When a plant possesses only one type of unisexual flowers, it is termed as a dioecious plant.
e.g. mulberry, date palm, etc.
Polygamous plants
Some plants possess three types of flowers bisexual, staminate and neuter.
They are called polygamous plants e.g., mango.
Insertion of Floral Leaves:
The position and arrangement of rest of the floral whorls (leaves) with respect to gynoecium on the thalamus is known as insertion of floral leaves.
It is of following three types:
1. Hypogyny:
When thalamus is convex or becomes conical in shape, gynoecium (ovary) occupies the highest position while the stamens, petals and sepals are inserted below the ovary,
the condition is known as hypogyny (hypo = below; gynoe = gynoecium)
The flower is called hypogynous.
The ovary is described as superior ovary,
e.g. Brinjal, Mustard, China rose, etc.
2. Perigyny:
When the thalamus forms a cupshaped or saucer-shaped structure with the ovary in the centre of it and the stamens, petals, and sepals, arise from the rim of cup or saucer,
thus are raised to a certain height so that they lie around the ovary, it is called perigyny (peri = around or surrounding)
Such flowers are said to be perigynous.
The ovary of a perigynous flower is described as superior or semi-inferior (half inferior).
e.g., rose, pea, bean, etc.
3. Epigyny:
In some flowers, the thalamus grows upward completely enclosing the ovary and may get fused with it, so that sepals, petals and stamens are developed from a region of the thalamus above the ovary.
The condition is known as epigyny (epi = upon or above).
In such a case, the flower is said to be epigynous and the ovary as Inferior ovary.
e.g., sunflower, Guava, etc.
