Flower and Its Parts
A flower is defined as a modified shoot in which nodes and internodes are highly condensed. The flower is the site of sexual reproduction. Id develops from the floral bud.
Parts of a Typical Flower
The flower is borne on a stalk called pedicel. The uppermost end of the pedicel is somewhat swollen. This swollen part of the pedicel is known as the thalamus. It bears all the four whorls of a flower;
Calyx: outermost whorl and consists green colour leaf like structure called sepals, manufacture food and protect the new delicate inner parts of the flower during the bud stage.
Corolla: Second whorl of flower, each segment of the corolla is called petal. Petal is bright in colour, sweet smell and nectar attract the insects which help in pollination.
Androecium: composed of one or more male reproductive organs called stamens, each stamen consists of a thin stalk or filament and two lobed head called the anther. The anther and the filament are connected by a connective tissue. Anthers produce pollen grains for pollination.
Gynoecium: composed of one or more female reproductive organs called carpels or pistils. Each carpel consists of an ovary, style and stigma.
Ovary: is basal swollen part bears the ovules and each ovule contains the female reproductive cell. The ovary of the flower develops into fruit and ovule becomes seeds after fertilization.
Style: is a thread like structure which connects the stigma with the ovary.
Stigma: is the terminal part, sticky, rough, hairy and receiving pollen grains during pollination.
Common Variations in Flower and Its Floral Parts
All 4 floral whorls present
Any one or more of floral whorl is absent
Both reproductive organs (stamens, carpels present)
(i)Staminate or male flower
(ii)Pistillate or female flower
(iii)On the basis of occurrence of unisexual flowers, plant is (a) Monoecious
Only one reproductive organ present
Only stamens present
Only carpel present
Both male and female flower occur on same plant, e.g. cucumber
Male and female flower occur on different plants, e.g. papaya
Both stamens and carpels are absent
Actinomorphic (regular) flower
Divisible into two equal halves by any radial plane e.g. mustard
Zygomorphic (irregular bilateral) flower
Divisible into two equal halves by a single vertical plane e.g. pea
It cannot be divided into two similar halves in any vertical plane e.g. Canna
A. Variations in Sepals and Petals
Polysepalous and Polypetalous (poly-free): sepals and petals are respectively free.
Gamosepalous and Gamopetalous (gamo-united): sepals and petals are respectively fused.
Perianth: Sepals and petals not distinguishable e.g. onion.
B. Variations in Stamens
Stamens show variation in their cohesion (fusion);
Monadelphous: stamens united by their filaments forming one group, (anthers free), e.g. China rose.
Diadelphous: stamens united by their filaments forming two groups, (anthers free), e.g. pea.
Polyadelphous: stamens united by their filaments forming two or more groups, e.g. lemon.
Syngenesious: stamens are united by their anthers and filaments are free, e.g. sunflower.
Synandrous: stamens united by both filaments and anthers, e.g. pumpkin.
Epipetalous: stamens united with the petals, e.g. Brinjal.
Epiphyllous: stamens united with the perianth leaves, e.g. onion.
Didynamous: four stamens, two short and two long, e.g. Tulsi.
Tetradynamous: Six stamens, inner four are long and outer two are short, e.g. mustard.
C. Variation in Carpel
On the basis of number of carpels, flowers may be;
Monocarpellary: having one carpel, e.g. pea.
Polycarpellary: having many carpels, e.g. China rose. It may be;
Syncarpous: carpels are fused, e.g. tomato.
Apocarpous: carpels are free, e.g. lotus.