5.5.1 Parts of a Flower
Each flower normally has four floral whorls, viz., calyx, corolla, androecium and gynoecium (Figure 5.10).
5.5.1.1 Calyx
It 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).
5.5.1.2 Corolla
It is composed of petals.
Petals are usually brightly coloured to attract insects for pollination.
Like calyx, corolla may also be gamopetalous (petals united) or polypetalous (petals free).
The shape and colour of corolla vary greatly in plants. Corolla may be tubular, bellshaped, funnel-shaped or wheel-shaped.
Perianth Callyx and Corolla are non-sterile parts of a flower and are called perianth. The term is used when these parts cannot easily be classified as either. It's unit is called as Tepal.
Aestivation
It is the mode of arrangement of sepals or petals in floral bud with respect to the other members of the same whorl.
The main types of aestivation are valvate, twisted, imbricate and vexillary (Figure 5.11).
Valvate
Sepals or petals in a whorl just touch one another at the margin, without overlapping.
eg Calotropis
Twisted
One margin of the appendage overlaps that of the next one and so on.
eg china rose, lady’s finger, cotton.
Imbricate
Margins of sepals or petals overlap one another but not in any particular direction.
eg Cassia, gulmohur.
Vexillary or Papilionaceous
There are five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel)
eg pea, bean
5.5.1.3 Androecium
andr - men + oîkos - house, home + eum (noun suffix) — more at vicinity
It is composed of stamens.
Each stamen which represents the male reproductive organ consists of a stalk/ filament and an anther.
Each anther is usually bilobed and each lobe has two chambers called the pollen-sacs.
The pollen grains are produced in pollen-sacs.
A sterile stamen is called staminode.
Stamens 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 lily.
There may be a variation in the length of filaments within a flower, as in Salvia and mustard.
5.5.1.4 Gynoecium
gyn - women + oîkos - house, home + eum (noun suffix) — more at vicinity
It is the female reproductive part of the flower and is made up of one or more carpels.
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.
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.
After fertilisation, the ovules develop into seeds and the ovary matures into a fruit.
Placentation:
It is the arrangement of ovules within the ovary.
The placentation are of different types namely, marginal, axile, parietal, central, free central and basal (Figure 5.12).
Marginal placentation: Placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows. eg pea
Axial placentation: The placenta is axial and ovules are attached to it in a multilocular ovary. eg china rose, tomato, lemon.
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