Gynoecium:
It is the female reproductive whorl of a flower and is also called pistil. Gynoecium is the innermost and fourth whorl of the flower and is made up of one or
more carpels.
Each carpel represents a modified (evolved) female reproductive leaf called megasporophyll which produces megaspores or female spores.
When the pistil consists of a single carpel, it is called a monocarpellary gynoecium or simple pistil.
e.g. pea, gram, etc.
When the gynoecium has two or more carpels, it is known as a polycarpellary gynoecium or compound pistil.
It may be
bicarpellary (two carpels, e.g. Datura),
tricarpellary (three carpels, e.g. Cucurbita),
pentacarpellary (five carpels e.g. Hibiscus).
When the carpels of a gynoecium are fused with each other then it is called syncarpous gynoecium, (China rose).
However, when the carpels of a gynoecium are free from each other, it is called apocarpous gynoecium e.g. rose.
Each carpel consists of three parts,
1. ovary,
2. style
3. stigma.
Ovary is the basal, swollen, fertile part of the carpel.
If there is only one carpel, the ovary is unilocular (locule = chamber),
if there are two, three or five carpels, fused with each other, i.e. polycarpellary, syncarpous condition, then the ovary is bilocular, trilocular or pentalocular respectively.
Each chamber of ovary contains one to many, small, globular structures called ovules or megasporangia.
Ovules are produced on a soft fertile tissue called placenta.
They exhibit different modes of arrangement within the ovary. It is called Placentation.
Style is a narrow, elongated, thread like (tubular) structure that connects ovary with stigma.
Stigma is the terminal part of the carpel.
- It receives pollen grains during pollination.
- It also provides place for pollen germination.
- Stigma is generally rough and sticky in nature.
Placentation:
Placentation may be defined as the mode of arrangement of ovules on the placenta within the ovary.
Following types of placentation are generally seen in different plants.
i) Marginal
When ovules are borne at the fused margins of unilocular ovary, it is called marginal placentation.
e.g. pea, bean, etc.
ii) Axile
When ovules are produced on the central axis of a multilocular ovary, it is known as axile placentation
e.g. China rose.
iii) Parietal
When ovules are borne on the inner wall of unilocular ovary of multicarpellary, syncarpous gynoecium, it is called parietal placentation,
e.g. Papaya, Cucumber.
iv) Basal
When a single ovule is borne at the base of an unilocular inferior ovary, it is known as basal placentation.
e.g. Sunflower
