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Flower Structure and
Function
Flowering plants are the
dominant type of plants on the earth today (there are about 250000
species). Flowers are therefore the most common
plant organs for sexual reproduction.
Flowers produce gametes
(sex cells).
Flowers play a key role in pollination.
Pollination is the transfer of pollen (containing the male gametes),
from the anther of a flower, to the stigma (receptive surface of the
female part of the flower) of the same or a different flower.
Parts of the Flower:
|
Flower Part |
Form
and Function |
| Peduncle |
Flower stalk. |
| Receptacle |
Part of flower
stalk bearing the floral organs, at base of flower. |
| Sepal |
Leaf-like
structures at flower base, protects young flower bud. |
| Calyx |
All the sepals
together form the calyx. |
| Petal |
Located in and
above the sepals, often large and colourful, sometimes scented,
sometimes producing nectar. Often serve to attract pollinators to
the plant. |
| Corolla |
All the petals
together form the corolla. |
| Stamen |
Male part of
the flower, consisting of the anther and filament,
makes pollen grains. |
| Filament |
The stalk of
the stamen which bears the anther. |
| Anther |
The pollen
bearing portion of a stamen. |
| Pollen |
Grains
containing the male gametes. Immature male gametophyte with a protective
outer covering. |
| Carpel\Pistil |
Female part of
the flower. Consisting of the stigma, style and ovary. |
| Stigma |
Often sticky
top of carpel, serves as a receptive surface for pollen grains. |
| Style |
The stalk of a
carpel, between the stigma and the ovary, through which the pollen
tube grows. |
| Ovary |
Enlarged base
of the carpel containing the ovule or ovules. The ovary
matures to become a fruit. |
| Ovule |
Located in the
ovaries. Carries female gametes. Ovules become seeds on fertilization. |
The sex of a flower can
be described in three ways:
-
Staminate
flowers: Flowers bearing
only male sex parts. These are sometime referred to as "male
flowers".
-
Carpellate\Pistillate
Flowers: Flowers bearing
only female sex parts. These are sometimes referred to as "female
flowers".
-
Hermaphhrodite\Complete
flowers: Flowers bearing
both male and female sex parts.
In many
cases flowers are borne as a group on a common stalk, called an inflorescence.
They are many different types of floral inflorescences. The type of
inflorescence present is sometimes used to aid in classifying flowering
plants. Below are a number of common floral inflorescences.
Flowers
are sometimes associated with prominent, often brightly coloured leaves
called bracts. In some instances (like in bougainvilleas,
heliconias and ginger lillies), the bracts are even more colourful and outstanding than
the flowers they surround.
|
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In the heliconia
cultivar on the left, the large yellow and red structures are bracts,
while the small yellow structures within them are the actual
flowers. |
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The yellow shrimp
plant, has large, showy yellow bracts, and smaller white flowers. |
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