In botany|lang=en terms the difference between flower and involucel

is that flower is (botany) a reproductive structure in angiosperms (flowering plants), often conspicuously colourful and typically including sepals, petals, and either or both stamens and/or a pistil while involucel is (botany) an involucre that forms at the base of a flower cluster within a compound inflorescence.

As nouns the difference between flower and involucel

is that flower is a colorful, conspicuous structure associated with angiosperms, frequently scented and attracting various insects, and which may or may not be used for sexual reproduction or flower can be something that flows, such as a river while involucel is (botany) an involucre that forms at the base of a flower cluster within a compound inflorescence.

As a verb flower

is to put forth blooms.