As nouns the difference between flower and ephemeral

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 ephemeral is something which lasts for a short period of time.

As a verb flower

is to put forth blooms.

As a adjective ephemeral is

lasting for a short period of time.