Floral symmetry refers to whether or not, and how, a flower can be segmented into mirror images of itself.
Angiosperms (flowering plants) use a wide variety of structures, colors, and aromas to attract pollinators. These non-reproductive parts of a flower are called the perianth. The perianth consists of the petals (corolla) and the green cuplike structure at a flower’s base, called the sepals, or calyx.
Looking at a flower from above, if you were to cut it in half, through the perianth, the two halves might be relatively identical, identical only along one plane, or not identical at all. These different types of symmetry are called radial, bilateral, or asymmetrical, respectively.
Snowflakes and apple pies have radial symmetry. No matter how you cut them in half, both halves look the same. Flowers with radial symmetry are called ‘regular’ or actinomorphic. Actinomorphic also refers to ‘regular’ star-shaped flowers that can be divided into three or more identical sections. Each section looks the same, no matter how you rotate the flower. Even though each half may not contain a complete petal, they are still considered actinomorphic.
Most people have bilateral symmetry. This means our left and right sides look very much alike, but our fronts and backs look very different. Some flowers, such as orchids and snapdragons, are the same way. Some flowers have only one line that can be cut to create a mirror image. These flowers are classified as ‘irregular’ or zygomorphic. Zygomorphic flowers have bilateral symmetry and that line is called the sagittal plane. Lavender, olive, sage, mint, nasturtiums, basil, and rosemary flowers are zygomorphic.
Simple v. compound flowers
Flowers can be simple or compound, but don’t let the names fool you. Simple, or primitive, flowers, such as strawberries and geraniums, are actually more complicated than compound flowers. Simple flowers usually have 3 to 6 petals, sepals, stamens and pistils. Compound flowers, called inflorescences, are made up of hundreds or thousands of flowers, each with only one or two sepals and petals. To analyze compound flowers for symmetry, you would have to look at individual florets from that inflorescence. While sunflowers and dandelions may appear to exhibit radial symmetry, the actual florets may or may not be symmetrical, depending on the species.
Go take a closer look at the flowers in your garden. What sort of symmetry do you see?
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