One of the many reasons that "flowers can look so different-their shape,colors, size, smells" has to do with the fact that flowers are the important reproductive part of the plant. In order for most plants to reproduce the flower needs to be pollinated. If they are not pollinated seeds are not produced. In many cases pollination is done by insects, birds or other animals. So it is important that the pollinators can find and have access to the flower in order to pollinate it. The size and shape of the flower is important to allow access to the pollinator and to exclude other organisms. The smell and color helps make it easier for the pollinator find that particular type of plant. Smell and color work like a sign to the pollinator that says "I am a Rose" and attract the pollinator.

One reason flowers look so different is that they are trying to attract pollinators like bees, hummingbirds, and even bats.These pollinators move pollen from one flower to another. This is how many plants reproduce. (What is pollen?) Of course if the pollinators did this "for free" instead of hunting for food they would go extinct. The plants "pay" the pollinators by making nectar (what is nectar?) for the pollinators to eat. A system like this is called "mutualism" because both participants benefit from it.

In order to advertise their nectar, they have distinctive colors and shapes that signal their special pollinators where they are. For example, hummingbirds are attracted to red colored things. Plants with long flowers that must be pollinated by long billed hummingbirds are red to advertise their nectar rewards. This attracts the hummingbirds. Other flowers have distinctive colors or shapes that attract bees, or other insects. Flowers that use bats as pollinators are usually white and open only at night. Why is it important for the plant to only attract pollinators that will go to another
plant of the same species?

Thanks for asking!