As nouns the difference between carpel and sepal

is that carpel is one of the individual female reproductive organs in a flower. A carpel is composed of an ovary, a style, and a stigma, although some flowers have carpels without a distinct style. In origin, carpels are leaves (megasporophylls) that have evolved to enclose the ovules. The term pistil is sometimes used to refer to a single carpel or to several carpels fused together while sepal is one of the component parts of the calyx, when this consists of separate (not fused) parts.