Flowers were developed by land plants. Showy petals and sweet nectar are often produced to lure insects to the blossoms. Insects carry the pollen from flower to flower, ensuring exchange of the information encoded in the chromosomes. Flowers have a well-defined structure. When the bud appears on the stem, we see the green sepals.
Sepals are the green parts that protect a flower bud before it opens.
There is usually one sepal for each petal. After the flower opens the sepals can still be seen behind the petals. Nectar is secreted at the base of the petals on the inside of the flower. The nectar is used to lure insects to the flower, and it is placed so that the insects get a dusting of pollen as they crawl to the nectar and lap it up. Then the insects fly off to other flowers, taking the pollen from the first flower with them.