A calyx is the outer protective covering of a flower bud, made up of small leaf-like parts called sepals. Before a flower opens, the calyx wraps around and shields the delicate petals inside, like a green jacket protecting what's underneath. You can see the calyx clearly on a rosebud: those green, pointed parts holding the bud closed are the sepals that form the calyx.

Once the flower blooms and the petals open, the calyx usually stays attached at the base of the flower. On a strawberry, that leafy green crown at the top is actually the calyx. Some flowers have colorful calyxes that look almost like petals themselves, but most are green and blend into the stem.

Botanists (scientists who study plants) use calyx to describe this part of nearly every flowering plant, from the tiniest wildflower to the largest magnolia blossom.