Section II. Floral Terminology

Sometimes we need more information about floral structure and parts to fully identify a flowering plant. Biologists use specific terminology relating to flower parts and how they are organized when distinguishing among different types of plants. We will cover some common terms that will be useful later in this Activity when you identify flowers on your own.

Flowers are described as complete when they possess all four appendages described above: sepals, petals, stamens, and carpels. Flowers missing any of these four parts are termed incomplete.

Complete Flower Incomplete Flower
Complete Flower Incomplete Flower

Another way to categorize flowers is by the presence or absence of male or female reproductive parts. Perfect flowers have both stamens and carpels, even if other parts are missing. If a flower has either stamens or carpels, but not both, it is termed imperfect or unisexual. The incomplete flower pictured above is an example of an imperfect flower. Which flower part is missing?

Symmetry is a third characteristic used to distinguish among flowers. In irregular flowers, the perianth parts (often the petals) are dissimilar so that the flower can be divided into equal halves only along one vertical plane down the middle. Such flowers have bilateral symmetry.

Image of orchid with line separating right and left sides
The Lady-slipper shows irregular symmetry.

In regular flowers the perianth parts are similar in size and shape so that the flower can be divided into equal halves by a vertical plane along any of various directions. This type of flower is said to have radial symmetry.

Image of Wild Radish showing regularity
Wild radish shows regular symmetry.

Both of these arrangements are directly related to pollination mechanisms possessed by specific plants.

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