What is the collective name for a flower's sepals?

The collective name for a flower’s sepals is the calyx.

Sepals are usually the green, leaf-like parts forming the outermost floral whorl. Their main job is to protect the developing flower while it is still a bud. After the flower opens, they may support the petals, remain beneath the fruit, or disappear depending on the species.

The calyx and the petals together make up the perianth, the non-reproductive covering of a flower. In many flowers, sepals are separate, but they can also be fused into a tube or cup. In some plants, sepals are brightly coloured and perform functions commonly associated with petals, helping attract pollinators.

The term “corolla” refers collectively to the petals, not the sepals. “Androecium” means the whorl of stamens, while “gynoecium” means the female floral parts, usually carpels. “Calyx” is therefore the specific botanical term for all the sepals considered together.