The Anatomy of a Petunia

Calyx

• The calyx, the petunia flower's outermost whorl, grows right on top of the pedicle or stem, and acts as the base for the entire blossom. It consists of yellow or green leaf-like structures known as sepals, which either grow separately or are fused in a cup-like formation. Because the sepals contain chlorophyll, they also serve as supplementary food synthesizers for the plant. Their main function, however, is to act as a protective enclosure for the growing bud.

Corolla

• As is the case with most flowers, the petunia's corolla is its most distinctive and conspicuous whorl, consisting primarily of the petals. Although the corolla's appearance varies according to breed, it serves the same general functions: to attract pollination agents and to protect the flowers' reproductive parts. The corolla is either poly- or gamopetalous, depending on whether the petals grow separately or are fused together. This whorl, together with the calyx, forms the perianth.

Stamens

• The stamens, known collectively as the androecium, comprise the flower's male reproductive organ. Each petunia flower contains multiple stamens, each of which has two parts: the anther and the filament. The two-lobed or capsule-shaped anther produces the flower's pollen. The stalk-like filament, on the other hand, serves as support for the anther, holding it aloft in the position most suited for pollen transfer.

Pistil

• The pistil or gynoecium, the innermost whorl, is the petunia's female reproductive organ. It consists of three parts: the ovary, the stigma and the style. The ovary, a cavity, produces and holds the flower's egg cells, which await pollination and fertilization from the pollen trapped in the sticky stigma. The style is to the stigma what the filament is to the anther: It holds it up in the optimal position for pollination. The petunia is an example of a complete or hermaphroditic flower, as it contains both male and female reproductive parts.