The different shapes of flowers help to ensure that they are fertilized. Flowers that rely on insects for pollination must make sure that the insect is carrying pollen from the same kind of plant. The shape of the flower ensures that only certain kinds of insect can pollinate it. Flat flowers, such as daisies and sunflowers, can be visited by hoverflies and some bees. Flowers that are formed into tubes only attract insects that have long tongues. As flowers bloom at different times of the year, there are usually only a few different species available to each insect at any one time, so the chances of pollination are increased.
The flowers of plants have evolved to permit the transmission of pollen and (hopefully) its eventual reception by an appropriate ovum of the same species. Many flowers have evolved to attract pollinators (mostly insects, bird and bats) with a nectar reward and are colored or structured to be attractive only to a few (or a single) pollinator to increase the odds of successful pollen transmission. For example, red flowers (and fruits) are attractive to birds, yellow to bees, blue to butterflies, and white to moths and bats.
In addition, the size and structure of the flower contributes to the type of fruiting bodies. Fruits can be a source of nutrients for some seeds, but they are also often a means of dispersing the seeds. Many fruits are palatable only to certain animals, and evolved to prevent damage to the seeds while the fruit is digested. Some plant species require that an animal erode the outside of the fruit or seed in its digestive tract, or else to break the fruit open.
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