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Flower Symmetry The typical angiosperm flower is constructed of floral organs in sets of whorls. This usually results in flowers with radial (actinomorphic) or bilateral (zygomorphic ) symmetry. Sepal whorl Actinomorphic Petal whorl Stamen whorl Stamen whorl Petal whorl Pistil whorl Sepal whorl Pistil whorl Trillium Back to main flower menu Next Back to flower organization menu Main menu Flower Symmetry Actinomorphic versus Zygomorphic flowers Actinomorphic flowers have a radial symmetry where the flower can be divided equally on more than one plane. Each half is a mirror image in three planes. Each half is a mirror image in only one plane. Spring starflower (Ipheion ) Back to main flower menu Zygomorphic flowers have bilateral symmetry where the flower can be divided equally in only one plane. Zygopetalum Back Next Back to flower organization menu Main menu Flower Symmetry Actinomorphic, radial flower symmetry appears to be an ancestral flower trait and is seen in all members of the ANITA Grade group of basal angiosperms. ANITA Grade group refers to the first letter for each of the original families (Amborellaceae, Nymphaeaceae, Illiciaceae, Trimeniaceae, and Austrobaileyaceae) described as basal angiosperms. Back to main flower menu Back Amborella Nymphaea Cabomba Illicium Next Back to flower organization menu Main menu Flower Symmetry Zygomorphic flowers with bilateral symmetry appears to have evolved several times even in the same family. It provides greater diversity and complexity in flower design and is associated with attracting specific pollinators. Lamiaceae Orchidaceae The zygomorphic flower form is often associated with advanced plant families. Fabaceae Back to main flower menu Back Next Scrophulariaceae Back to flower organization menu Main menu Flower Symmetry Peloric mutations A peloric mutation causes a flower that is normally zygomorphic with bilateral symmetry to become more actimorphic with apparent radial symmetry and petals with similar size and shape. Zygomorphic Peloric mutation African violet flowers normally have bilateral symmetry. A peloric mutation in African violet (Saintpaulia). Back to main flower menu Back Next Back to flower organization menu Main menu Flower Symmetry Peloric mutations The term peloric was first used by Linnaeus to describe this phenomenon. Peloric is Greek for “monster”. This mutation in cape primrose causes all the petals to become similar in shape and size. Typical normal flower Peloric mutant A peloric mutation in cape primrose (Streptocarpus). Back to main flower menu Back Next Back to flower organization menu Main menu Flower Symmetry Peloric mutations A peloric mutation in members of the Asteraceae can cause the ray florets to become tubular and have radial symmetry as seen in this selection of Gaillardia. Typical zygomorphic ray florets Back to main flower menu Back Next Peloric mutation Back to flower organization menu Main menu Flower Symmetry Peloric mutations The genes responsible for the zygomorphic flower form have been found in snapdragon (Antirrhinum). The differential gene expression of CYCLOIDEA and DICHOTOMA determines petal form in normal bilateral flowers. Loss-offunction mutations in these genes causes a loss of the zygomorphhic form. Typical flower form Back to main flower menu Back Peloric mutant Back to flower organization menu Main menu
