A flower is the reproductive structure of an
angiosperm (flowering plant). Its function is to mediate the fusion of the
sperm (male gamete) and ovule (female gamete) for production of seeds. The
arrangement of flowers in a stalk is called inflorescence.
In flowering plants, the process of reproduction starts with pollination
(transfer of pollen to stigma), followed by fertilization (fusion of sperm and
ovule) and formation of seeds. Some flowers exhibit certain designs to attract
pollinating agents such as bees and butterflies, which in turn facilitate
fertilization. Depending upon the pollinating agent, flowers can be categorized
into anemophilous (pollinated by wind, e.g. grasses), hydrophilous (pollinated
by water, e.g. seagrass) and entomophilous (pollinated by insects, e.g.
A flower can be studied as a modified shoot in which the apical meristem does
not grow continuously, showing determinate growth. In this, the stem of the
flower is the pedicel (flower stalk) and the flower parts are arranged at the
end of the pedicel, also called the torus or receptacle. The four major parts
or whorls of a flower, starting from the base of the receptacle are calyx,
corolla, androecium and gynoecium.
Calyx (Sepal): Calyx are the outermost whorl of sepals in a flower,
which protects the flower before it opens. In general, calyx are green in
color. However, in some plant species, they are modified like the color of
petals. In such a case, the sepals are referred to as petaloid sepals. Flowers
can be classified into two types, based on whether the sepals are free or
fused. Flowers with free sepals are called polysepalous flowers; whereas, those
with fused sepals are called gamosepalous flowers.
Corolla (Petal): Corolla represents the whorl of petals. Petals are
usually colorful, and serve the purpose of attracting insects for pollination.
Like sepals, petals can be either free or fused in a flower. Flowers with free
petals are called polypetalous flowers; whereas, gamopetalous flowers have
Androecium: Androecium or the stamen is the male reproductive organ
in a flower. A stamen consists of an anther and a filament. An anther produces
and contains pollens; whereas, the filament is a hair like structure that
attaches the anther to the flower. The pollen contains the male gametes or the
Gynoecium: The female reproductive organ of a flower is called the
gynoecium, which consists of one or more pistils. It is usually located in the
center of the flower. A pistil consists of three structures viz. ovary that
produces ovules, style (a stalk that connects ovary and stigma) and the stigma
that receives the pollen during fertilization.
Flowers are of different types, classified depending upon the presence or absence of
the major parts. A flower consisting of all the four major parts is called
complete flower. If any of the major whorls is lacking, then it is referred to
as an incomplete flower. Besides these, a flower having both male and female
organ is called a perfect flower, for e.g. roses, hibiscus; whereas, a flower
with only one reproductive organ is called an imperfect flower, for e.g.
flowers of pumpkin or cucumber plants.