Flower variations in structure
Like virtually all forms in nature, flowers display many variations in their structure. Most flowers have all four whorls—pistil, stamens, petals, and sepals. Botanists call these complete flowers. But some flowers are incomplete, meaning they lack one or more whorls. Incomplete flowers are most common in plants whose pollen is dispersed by the wind or water. Since these flowers do not need to attract pollinators, most have no petals, and some even lack sepals. Certain wind-pollinated flowers do have small sepals and petals that create eddies in the wind, directing pollen to swirl around and settle on the flower. In still other flowers, the petals and sepals are fused into structures called a floral tube. Flowers that lack either stamens or a pistil are said to be imperfect. The petal-like rays on the edge of a sunflower, for example, are actually tiny, imperfect flowers that lack stamens. Imperfect flowers can still function in sexual reproduction. A flower that lacks a pistil but has...