"to come into flower," 1775, from Latin efflorescere, inceptive form (in Late Latin simplified to efflorere) "to blossom, spring up, flourish, abound," from assimilated form of ex "out" (see ex-) + florescere "to blossom," from flos "flower" (from PIE root *bhel- (3) "to thrive, bloom"). Sense in chemistry is from 1788.
