Most
flower families can be placed in one of three groups, based on
symmetry, or lack of it, in the flowers. Some flowers are radially
symmetrical. In other words, the flowers look the same when rotated,
just as a wheel looks the same when turned on its axle. Other
flowers are bilaterally symmetrical, the left side being a mirror
image of the right, just like a face. In still other flowers there
is no obvious symmetry, either because the flowers are tiny and
inconspicuous, often lacking petals, or because the flower parts
are arranged very irregularly. A few families contain both radially
and bilaterally symmetrical species. In that case, the family
is placed in the symmetry group most common to the family. Thus,
snapdragons, usually bilaterally symmetrical, are classified in
that group. But the speedwells, members of the Veronica genus
within the snapdragon family, and more or less radially symmetrical,
are mentioned in the list of radially symmetrical families so
that the snapdragon family can be searched when a more or less
radially symmetrical four-petaled flower is to be identified.
Radially
symmetrical flowers are then further subdivided by the number
of petals usual in each family. (In most families the number of
petals is constant, the most notable exceptions being the composite,
buttercup and poppy families.) The most characteristic features
of each family are given in each petal number section. Thus, a
radially symmetrical flower with paired opposite leaves and five
petals, each notched at the tip, is likely a member of the pink
family. If the flowers are tiny and arranged in umbels (umbrella-like
clusters), it is likely a parsley family member. If flowers are
tiny with four petals, and the stem is square, the bedstraw family
should be searched. Similar clues to family identification are
provided in the list of bilaterally symmetrical families. For
example, if the stem is square the flower is probably a mint.
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