Page 165 - Biology_F5

Biology for Advanced Level Secondary Schools

Flower symmetry
A flower can be dissected longitudinally
to expose its internal parts for clear
examination. One of the fundamental
Line of
aspects of a flower plan is its overall symmetry
shape, which is described as symmetry.
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A symmetrical flower is the one that
can be divided along at least one plane
in relation to perianth into two or more
identical parts, which are mirror image of Figure 3.36: Structure of an actinomorphic
each other. Although most flowers have flower
a certain kind of symmetry, few flowers (b) Bilateral symmetry
have no symmetry and are referred to as A flower is said to be bilaterally symmetrical
asymmetrical flowers. Three categories of when it can be split into two identical halves
flowers’ symmetry are therefore recognised in one plane only. This type of symmetry
namely, radial symmetry or actinomorphic is caused by differences in size and shape
flower, bilateral symmetry or zygomorphic of petals and or sepals as can be noted
flower and asymmetric flower.
in pea and bean flowers. Additionally, in
some flowers, some whorls may be fused
(a) Radial symmetry or some parts of an individual whorl may
A flower is said to be radially symmetrical have different sizes compared to others in
when it can be split vertically through the the same flower (Figure 3.37). Bilaterally
centre in any one of several planes to produce symmetrical flowers are said to be irregular
identical parts, which are mirror images of or zygomorphic. Example sweet pea. The
each other. This type of symmetry applies symbol used to represent them is ●|●.
when each part of the whorl is identical
with all other parts. Normally each side
can have one sepal and one petal. Radially
symmetrical flowers are said to be regular
or polysymetric or actinomorphic (Figure
3.36). Literally, actinomorphic means star
like because the flower can be divided
into three or more identical parts. Most
flowers are actinomorphic, for instance the
Hibiscus flower. The symbol used to denote
this type of symmetry is .

Figure 3.37: Zygomorphic flower

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