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Introduction to Flowers
A flower is a specialized shoot in which the leaves have been modified into floral
structures. When we talk about flowers, we might think of roses or sunflowers, each
with its unique appeal. Flowers consist of four main parts, also known as whorls.

Flower Anatomy

Pedicel
The pedicel is the stalk of the flower, the part you hold. A flower with a pedicel is
called pedicellate. Not all flowers have a pedicel; those lacking one are sessile.

Receptacle (Thalamus)
The pedicel expands into a cup-shaped structure called the receptacle or thalamus.

The thalamus holds all four whorls (parts) of the flower: calyx, corolla,
androecium, and gynoecium.

Visually, the structure looks like: the pedicel extends into a cup shape (the
receptacle), which then holds the stamen (androecium), corolla (petals), sepals
(calyx), and carpels (gynoecium).

Whorls of a Flower
The four whorls of a flower include:

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Calyx: Collection of sepals. Sepals are the outermost, usually green, parts of
the flower.
Corolla: Collection of petals. Petals are the often brightly colored parts of the
flower.
Androecium: Collection of stamens, the male parts.
A stamen has a thread-like filament with a bilobed anther at the tip.
Inside the anther, there are pollen grains.
Gynoecium: Collection of carpels, the female parts.
A carpel consists of the ovary, style (a tube-like structure), and stigma
(the top part).
The stigma, style, and ovary make up the pistil.

Complete vs. Incomplete Flowers

Complete (Perfect) Flower: Has all four whorls (calyx, corolla, androecium, and
gynoecium).
Incomplete (Imperfect) Flower: Missing one or more of the four whorls.
A sunflower is an inflorescence (a collection of flowers), not a single
flower.

Essential vs. Non-Essential Parts

Essential Parts: Directly involved in reproduction (androecium and gynoecium).
Non-Essential Parts (Accessories): Not directly involved in reproduction but
support it (e.g., sepals and petals).
Accessories protect the reproductive parts.

Think of it like buying a car: the engine is essential, while side mirrors or a sound
system are accessories.

Variations in Sepals and Petals

Sometimes, sepals and petals can look alike:

Perianth: When sepals and petals are indistinguishable.

Seploids: When sepals and petals are green. The sepal color has bled into the
petal color.
Petaloid: When sepals are colored like petals (i.e., not green).

Bracts

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Flowers sometimes originate from the axil (the point where a leaf joins the stem). A
bract is a leaf-like structure found where the flower originates. It can be green or
colored.

For example, bougainvillea has leaf-like structures (bracts), while the actual flower is
inside. Bougainvillea are often used as bushes around property lines.## Flower
Anatomy and Reproduction

Nectaries and Nectar

Nectaries: Tissue or cells in a flower that produce nectar.
Nectar: A sweet, fragrant liquid produced by nectaries, attracting insects for
pollination.
Bees collect nectar and convert it into honey.
Nectaries are usually found at the base of the flower or pistil (female
part).

Parts of a Flower
1. Petals: Collection is called Corolla.
2. Sepals:
Green in color.
Collection is called calyx.
Also called the stalk of the flower.
Holds the flower.
The stalk is called the pedicel.
3. Nectaries.
4. Female Part (Gynoecium):
Ovary: A big, oval structure.
The outer structure that becomes the fruit after fertilization.
Ovule: The inner structure inside the ovary.
Becomes the seed.
Style: Located above the ovary.
Stigma: Located at the top.
5. Male Part (Androecium):
Anther: Contains pollen grains.
Filament: Holds the anther.

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Male vs. Female Flowers

Male Part: Stamen (anther produces pollen).
Female Part: Carpel (ovary holds ovules, which contain the egg).
Fertilization: The fusion of male and female gametes.

Flower Sexuality
Bisexual (Hermaphrodite) Flower: Contains both male and female parts (e.g.,
earthworm).
Unisexual Flower: Contains either male or female parts.
Staminate Flower: Contains only male parts (stamen).
Pistillate Flower: Contains only female parts (pistil).
Neutral Flower: Contains neither male nor female parts (e.g., ray florets of a
sunflower).

Calyx Details
Calyx: Collection of sepals.
Outermost part, protects the flower in the bud stage.
Gamosepalous: Sepals are fused together.
Polysepalous: Sepals are free or open.
Example: Hibiscus, which may have an epicalyx (an additional series
of sepals below the calyx).
Petaloid: Sepals are brightly colored instead of green.
Example: Gulmohar (Flame in the forest), a bisexual flower.

Corolla Details
Corolla: Collection of petals.
Modified leaves that protect the reproductive parts.
Brightly colored to attract insects for pollination.
Pollination: Transfer of pollen grains from anther to stigma.
Polypetalous: Petals are free.
Gamopetalous: Petals are fused, forming a tube-like structure.

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Androecium Details
Stamen: A thin, tube-like structure with a bilobed (two-lobed) anther at the
end.

Anther: Contains chambers with pollen sacs, which hold pollen grains
(male reproductive part).
Filament: Supports the anther.

Androecium: The collection of stamens.

Term Definition Example

Mono Single China Rose

Monadelphous All filaments are united into one group.

Filament Groupings
When filaments unite in bundles, several arrangements can occur:

Diadelphous: 2 tubes are formed. In this structure, filaments are united into
bundles, such as in the example of peas. A single stamen remains separate.
Polyadelphous: Multiple groups of filaments form separate bundles. An
example is the Bombax, a type of grass.

Carpel Structure
The carpel is located in the center of the flower and comprises three main parts:

Ovary: The female reproductive part, containing the ovules.

Style: An extension of the ovary.
Stigma: The top-most part of the style.

Together, the stigma, style, and ovary form the carpel, which is the female
reproductive organ.

The female reproductive gamete is the ovule inside the ovary, and the
male gamete is the pollen grain.

Ovary Chambers

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If you cut the ovary, you will see chambers called locules.

Locules: Chambers inside the ovary.

Placenta: Tissue that attaches the ovules to the ovary wall.
Ovules: Located inside the locules and will develop into seeds after fertilization.

Inflorescence
Inflorescence refers to the arrangement of flowers on the axis of a plant. Flowers can
be arranged in various ways, and this arrangement is known as inflorescence.

Placentation
Placentation describes how the ovules are arranged and attached to the ovary wall.

Placentation: The manner in which ovules are arranged and attached to

the ovary wall.

The ovary will eventually develop into the fruit, and the ovules will become seeds
after fertilization.

Pollination and Fertilization

Pollination: The transfer of pollen grains from the anther to the stigma.
Fertilization: The fusion of the male gamete (from the pollen grain) with the
female gamete (ovule).

Fertilization must occur for fruits to develop.

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