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

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 verticillaster is (botany) a whorl of flowers apparently of one cluster, but composed of two opposite axillary cymes, as in mint.

As nouns the difference between flower and verticillaster

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 verticillaster is (botany) a whorl of flowers apparently of one cluster, but composed of two opposite axillary cymes, as in mint.

As a verb flower

is to put forth blooms.