What is a gynoecium?
Gynoecium is most commonly used as a collective term for the parts of a pistillate flower that produce ovules and ultimately develop into the fruit and seeds. (1)
The gynecium is often referred to as the female portion of a pistillate flower. (1)

What does the gynoecium do?
produces megaspores

Where is the gynoecium located?
The gynoecium is the innermost whorl of a flower.

What does a gynoecium contain?
one or more pistils (1)
typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. (1)

Resources
1. https://en.wikipedia.org/wiki/Gynoecium

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