The calyx is the outermost whorl of a flower. It comprises sepals, tiny leaves present at the base of a flower. If the sepals are free the calyx is called polysepalous, and if they are united it is called gamosepalous.
The flowers whose sepals are fused or jointed sepals, either wholly or at the base only are called gamosepalous flower.
Hibiscus and Periwinkle are examples of gamosepalous flower.