A complex organ in phenogamous plants, comprising a group of reproductive organs and its envelopes. In the popular use of the word, the characteristic feature of a floweris the ‘coloured’ (not green) envelope, and the term is not applied where this is absent, unless there is obvious resemblance in appearance to what is ordinarily so called. In botanical use, a flower consists normally of one or more stamens or pistils (or both), a corolla, and a calyx; but the two last are not universally present.——牛津当代大辞典

a coloured or white part that a plant or tree produces before fruit or seeds.——朗文当代大辞典  @en