Which part of the flower serves as the protective structure outside the petals?

The sepal is the part of the flower that serves as the protective structure outside the petals. Its primary function is to enclose and protect the developing bud before it opens and also to provide support to the flower once it is fully formed. Sepals are usually green and leaf-like, helping to shield the more delicate petals from environmental factors and potential damage during the growth process. Understanding the role of the sepal enhances knowledge of flower anatomy and the ways in which different parts contribute to a plant's reproductive success.

The stigma is responsible for receiving pollen during fertilization, while the ovary contains the ovules and eventually develops into fruit. The filament is a part of the stamen that supports the anther, where pollen is produced. Each of these structures plays a critical role in the reproduction process but does not serve the protective purpose of the sepal.