CHAPTER-3

FLORAL BIOLOGY
The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction.
A typical flower has four different kinds of whorls (circular arrangement set of floral
organ) arranged successively on the swollen end of the stalk or pedicel, called thalamus or
receptacle . These are calyx, corolla, androecium and gynoecium. Calyx (whorl of sepals-
green protective) and corolla (whorl of petals- attracts pollinators) are accessory organs,
while androecium (whorl of stamens) and gynoecium (whorl of carpels/pistils) are
reproductive organs. In some flowers like lily, the calyx and corolla are not distinct and are
termed as perianth.
Note:
 If sepals and petals are distinct, the perianth is said to be heterochlamydeous.
 If sepals and petals are undifferentiated / similar in form, the perianth is called
homochlamydeous (e.g., in lilies, where the perianth parts are called tepals).

When a flower has both androecium and gynoecium, it is bisexual. A flower having either
only stamens or only carpels is unisexual. In symmetry, the flower may be actinomorphic
(radial symmetry) or zygomorphic (bilateral symmetry). When a flower can be divided into
two equal radial halves in any radial plane passing through the centre, it is said to be
actinomorphic, e.g., mustard, datura, chilli. When it can be divided into two similar halves
only in one particular vertical plane, it is zygomorphic, e.g., pea, gulmohur, bean, Cassia.
A flower is asymmetric (irregular) if it cannot be divided into two similar halves by any
vertical plane passing through the centre, as in canna. A flower may be trimerous,
tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5,
respectively. Flowers with bracts, reduced leaf found at the base of the pedicel, are called
bracteate and those without bracts, ebracteate.
Based on the position of calyx, corolla and androecium in respect of
the ovary on thalamus, the flowers are described as hypogynous perigynous and epigynous.
In the hypogynous flower the gynoecium occupies the highest position while the other
parts are situated below it. The ovary in such flowers is said to be superior, e.g., mustard,
China rose and brinjal. If gynoecium is situated in the centre and other parts of the flower
are located on the rim of the thalamus almost at the same level, it is called perigynous. The
ovary here is said to be
half inferior, e.g., plum, rose, peach. In epigynous flowers, the margin of thalamus grows
upward enclosing the ovary completely and getting fused with it, the other parts of flower
arise above the ovary. Hence, the ovary is said to be inferior as in flowers of guava and
cucumber, and the ray florets of sunflower.
Figure 1: Position of floral parts on thalamus: (a) Hypogynous (b) and (c) Perigynous (d)
Epigynous
Parts of a flower:
Each flower normally has four floral whorls, viz., calyx, corolla, androecium and
gynoecium

Calyx:
The calyx is the outermost whorl of the flower and the members are called sepals.
Generally, sepals are green, leaf like and protect the flower in the bud stage. The calyx may
be gamosepalous (sepals united) or Polysepalous (sepals free). Corolla is composed of
petals. Petals are usually brightly coloured to attract insects for pollination. Like calyx,
corolla may be also free

Figure 2 : Parts of a flower

(gamopetalous) or united (polypetalous). The shape and colour of corolla vary greatly in
plants. Corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped.Aestivation:
The mode of arrangement of sepals or petals in floral bud with respect to the other
members of the same whorl is known as aestivation. The main types of aestivation are
valvate, twisted; imbricate and vexillary (Figure.3). When sepals or petals in a whorl just
touch one another at the margin, without overlapping, as in Calotropis, it is said to be
valvate. If one margin of the appendage overlaps that of the next one and so on as in china
rose, lady’s finger and cotton, it is called twisted. If the margins of sepals or petals overlap
one another but not in any particular direction as in Cassia and gulmohur, the aestivation is
called imbricate. In pea and bean flowers, there are five petals, the largest (standard)
overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior
petals (keel); this type of aestivation is known as vexillary or papilionaceous.
Figure 3: Types of aestivation in corolla: (a) Valvate (b) Twisted (c)
Imbricate (d) Vexillary

Androecium:
Androecium is composed of stamens. Each stamen which represents the
male reproductive organ consists of a stalk or a filament and an anther. Each
anther is usually bilobed and each lobe has two chambers, the pollen-sacs.
The pollen grains are produced in pollen-sacs. A sterile stamen is called
staminode. Stamens of flower may be united with other members such as
petals or among themselves. When stamens are attached to the petals, they
are epipetalous as in brinjal, or epiphyllous when attached to the perianth as
in the flowers of lily. The stamens in a flower may either remain free
(polyandrous) or may be united in varying degrees. The stamens may be
united into one bunch or one bundle (monoadelphous) as in china rose, or
two bundles (diadelphous) as in pea, or into more than two bundles
(polyadelphous) as in citrus. There may be a variation in the length of
filaments within a flower, as in Salvia and mustard.

Gynoecium:
Gynoecium is the female reproductive part of the flower and is made up of
one or more carpels. A carpel consists of three parts namely stigma, style
and ovary. Ovary is the enlarged basal part, on which lies the elongated
tube, the style. The style connects the ovary to the stigma. The stigma is
usually at the tip of the style and is the receptive surface for pollen grains.
Each ovary bears one or more ovules attached to a flattened, cushion-like
placenta. When more than one carpel is present, they may be free (as in lotus
and rose) and are called apocarpous. They are termed syncarpous when
carpels are fused, as in mustard and tomato. After fertilisation, the ovules
develop into seeds and the ovary matures into a fruit