petal, one of the four basic parts of a flower, next innermost organ from the sepal. The whorl of petals is known collectively as the corolla [Lat.,=little crown]. The number of petals is usually constant within groups (e.g., five in the rose family), as are the numbers of the other organs. Identification by number is, however, complicated by various factors; the petals may be fused, inconspicuous, or entirely absent, in which case their role as the showy part of the flower is sometimes supplanted by modified leaves, the bracts, as in the dogwood and poinsettia, or by modified stamens, as in the canna and the lady's-slipper. Selective breeding can produce petallike stamens (e.g., in cultivated roses and geraniums) and so-called double flowers, i.e., varieties with more than the normal number of petals. Petals are usually brightly colored and often secrete perfume and nectar (in nectaries at the base of the petal) that attract insects and birds needed for cross-pollination. When fertilization has taken place the petals usually drop off; however, in some flowers they persist (see everlasting). In general there are fewer petals and their fusion is greater as the evolutionary development increases. Radially symmetrical arrangement also gives way to bilateral symmetry or even asymmetry.
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