The flower of a monocot has petals and sepals in multiples of three i.e 3,6,9 etc.The flower of a dicot has petals and sepals in multiples of four or five i.e 4,8,12 etc or 5,20,25 etc.
Flowers are intricate structures that contain the reproductive parts of plants. Completeness in the floral world doesn’t refer to the successful formation of flowers, but it defines blossoms that contain certain components. When a flower contains all four primary structures -- petals, sepals, stamens and a pistil -- it is botanically “complete.”
Plant sexual reproduction relies on stamens, which are the male parts, and pistils, which are the female parts. Stamens contribute the male genetic material in the form of pollen, which is produced from anthers that are on the terminal ends of stalks called filaments. Pistils form ovaries at their bases and stigmas, which are sticky pollen receptors, on the terminal ends of stalks called styles. Inside the ovaries, ovules are tiny structures that contain female genetic material. When fertilized, ovules form viable seeds that perpetuate second-generation flowers.
Supporting Structures
Petals and sepals protect and support plant reproductive structures as they develop. Multiple sepals, collectively called the calyx, form the outermost whorl of a flower. Sepals protect a flower bud before it opens and support it after it blooms. Sepals often resemble small green or brown leaves that are arranged around the base of flowers, but sometimes they are larger and more colorful like the petals. Multiple petals, collectively called the corolla, comprise the innermost whorl of a flower. Petals attract pollinators with their colors, fragrances and patterns.
Complete Flowers
Some plants produce separate male and female flowers; sometimes they're on the same plant and other times they're borne on different plants. When flowers contain both male and female parts within the same blossom, they are botanically “perfect” and do not require another plant for successful pollination. Some plants don’t form distinct petals and sepals, but they have one undifferentiated whorl comprised of structures called tepals. Petals, sepals, stamens and pistils are not formed on all flowers, but when they do the flower is said to be “complete.”