Lesson 6 of 13 · 6 min
Flower whorls and symmetry
NCERT §5.5, §5.5.1, Figure 5.10
Nithya picks a mustard flower, a pea flower and a canna from the garden fence and tries to cut each into two matching halves with a blade. The mustard works every way, the pea only one way, the canna not at all.
The lesson in notes
In short
The flower is the reproductive unit of angiosperms and serves sexual reproduction.
A typical flower has four whorls, one above another, on the swollen tip of the pedicel called the thalamus or receptacle: calyx, corolla, androecium and gynoecium.
Calyx and corolla are accessory organs; androecium and gynoecium are the reproductive organs.
When calyx and corolla cannot be told apart, as in lily, together they are called the perianth.
Bisexual flower: has both androecium and gynoecium. Unisexual flower: has only stamens or only carpels.
Actinomorphic (radial symmetry): any radial plane through the centre cuts it into two equal halves. Examples: mustard, datura, chilli.
Zygomorphic (bilateral symmetry): only one particular vertical plane gives two similar halves. Examples: pea, gulmohur, bean, Cassia.
Asymmetric (irregular): no vertical plane through the centre gives two similar halves. Example: canna.
Trimerous, tetramerous and pentamerous flowers have floral appendages in multiples of 3, 4 and 5.
A bract is a reduced leaf at the base of the pedicel. Flowers with bracts are bracteate; flowers without them are ebracteate.