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[Left] Normal Streptocarpus flower (zygomorphic or mirror-symmetric), and [right] peloric (radially symmetric) flower on the same plant. Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts.
In contrast, monosymmetrical, dorsiventral or zygomorphic flowers have bilateral symmetry and the evolution of their shape is related to the need to attract and guide pollinators to them, as for example, the flowers of orchids and many legumes.
Pelorism is the term, said to be first used by Charles Darwin, for the formation of 'peloric flowers' [1] which botanically is the abnormal production of radially symmetrical (actinomorphic) flowers in a species that usually produces bilaterally symmetrical (zygomorphic) flowers. [2] These flowers are spontaneous floral symmetry mutants.
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symmetry down its centre, or a pine cone displays a clear symmetrical spiral pattern.
Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed irregular or zygomorphic (meaning "yoke-" or "pair-formed"). In irregular flowers, other floral parts may be modified from the regular form, but the petals show the greatest deviation from radial symmetry.
The plants are annual and perennial herbs, as well as shrubs. Flowers have bilateral (zygomorphic) or rarely radial (actinomorphic) symmetry. The Scrophulariaceae have a cosmopolitan distribution, with the majority found in temperate areas, including tropical mountains.
Zygomorphic – one axis of symmetry running down the middle of the flower so the right and left halves reflect each other. Zygomorphy – the type of symmetry that most irregular flowers have, where the upper half of the flower is unlike the lower half, but the left and right halves tend to be mirror images of each other.
Symmetry or arrangement may be described for the whole flower; in such case the corresponding symbol is usually placed at the beginning of the formula. It may be also outlined separately for different organs, placing it after their labels or numbers, or it may not be included in the formula at all.