Young Brunette Girl Outside In Yellow Flowers

Although the arrangement described above is considered "typical", plant species show a wide variation in floral structure. These modifications have significance in the evolution of flowering plants and are used extensively by botanists to establish relationships among plant species.
In the majority of species, individual flowers have both functional carpels and stamens. These flowers are described by botanists as being perfect or bisexual. Some flowers lack one or the other reproductive organ and called imperfect or unisexual If unisex flowers are found on the same individual plant but in different locations, the species is said to be monoecious. If each type of unisex flower is found only on separate individuals, the plant is dioecious.
Additional discussions on floral modifications from the basic plan are presented in the articles on each of the basic parts of the flower. In those species that have more than one flower on an axis, the collection of flowers is termed an inflorescence. Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. The common example of this is most members of the very large composite (Asteraceae) group. A single daisy or sunflower, for example, is not a flower but a flower head—an inflorescence composed of numerous flowers (or florets).
Many flowers have a symmetry, if the perianth is bisected through the central axis from any point, symmetrical halves are produced—the flower is called regular or actinomorphic, e.g. rose or trillium. When flowers are bisected and produce only one line that produces symmetrical halves the flower is said to be irregular or zygomorphic. e.g. snapdragon or most orchids.