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How do carpels form the gynoecium of a flower?

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Bumblebee on teasel — Plant reproductive system A large bumblebee (*Bombus* species) pollinating a teasel flower head (*Dipsacus* species).

The gynoecium is the female reproductive part of a flower, composed of one or more units called carpels. These carpels are arranged on the floral axis either spirally, in more basal plant families, or in a single whorl in more advanced families.1

Carpels can exist in two primary configurations:
* Apocarpous: The carpels remain separate from one another.1
* Syncarpous: The carpels are fused together to form a compound ovary.1

In a syncarpous gynoecium, the fusion may involve only the ovaries, leaving the styles and stigmas free, or it may extend to include the styles, leaving only the stigmas separate. Each carpel typically contains an ovary at its base, which houses ovules, a style (a stalk), and a stigma at the top to receive pollen. The number of carpels in a syncarpous ovary generally corresponds to the number of internal cavities, or locules, within the structure.1