The sole purpose of the flower is to create seed, the means for the plant to multiply and extend its genetic code in a subsequent generation. Pollination of the flower is vital for that task. Although some plants are pollinated by wind or water, a tremendous number of flowers rely upon insects, birds and mammals to place the male pollen on the female stigma. Large, showy flower parts attract the attention and lure those animal pollinators.
The most famous and widely recognized part of a flower includes the petals. Usually large and colorful, these structures frame the important organs of the flower, attracting attention to pollinators and humans alike. Petals can vary in size depending on the plant species and which pollinating creature the flower is designed to attract. Small-sized flowers are engineered to attract small-sized insects that are well-matched to reach and pollinate the smaller floral parts. Hummingbirds are consistently attracted to petals that are red. Larger flowered plants that rely on mammals, such as monkeys or bats, for pollination may have extra petals or floral parts so that they are more readily seen.
Sepals are the modified leaves that protect the developing flower bud. Once the petals unfurl, the sepals are often hidden, seen only if the flower is inverted, and these usually green slivers support the bottoms of the petals. However, in some plant species, the sepals look exactly like the petals, having the same size and attractive colors. Lilies and orchids are two good examples---these plants' flowers often have only three petals, but also three sepals that may match the petals in size and shape, sometimes not. In ladyslipper orchids, the three petals are differently shaped, one looking like the tip of a moccasin shoe. Daylilies and waterlilies have sepals that match the look of the petals.
Bracts are a type of leaf that has been modified for a specific purpose. With regard to flowers, the bract is used to bring attention visually to the flowers that may be very tiny, lackluster in color, or are not quickly seen or detected by pollinators. Spurges have unimpressive, tiny flowers, but the bracts that grow next to or around them are larger and usually brightly colored. The poinsettia is perhaps the most famous example, with tiny yellow flowers surrounded by vivid red bracts, attracting attention. Often, bracts last significantly longer on the plant than the flower, lasting for weeks or months after the true flowers have been pollinated and even ripened to release their seeds.