Functions of Flower Sepals

Identification

• Most sepals are green leaflike structures that collectively make up the calyx of a flower. Some sepals may be showy and colorful and look like the flower petals instead of resembling leaves. You can find sepals at the base of a flower bud, just underneath the petals. Sepals are attached around a circular structure called the receptacle, which forms at the top of a flower stem. Some sepals are individually separated from each other on the same flower, while others form a fused cup.

Functions

• Flower sepals have varied functions. They encase the flower buds, protecting them by forming a barrier between the developing petals and the environment. Sepals help prevent insects and diseases from reaching the flower bud, and they block sunlight and inclement weather from causing damage to the tender petals. Because the sepals contain chlorophyll, they are able to perform photosynthesis, which produces food for the plant. Some sepals, which are called tepals, attract pollinators because they are colorful like the flower petals.

Mechanism

• Sepals may zip open quickly or peel down gradually to allow the mature flower petals to open. California poppy flowers (Eschscholzia californica), which grow as perennials in U.S. Department of Agriculture plant hardiness zones 6 through 10, open instantly when their sepals split apart. Environmental triggers, such as light and temperature, prompt the sepals on different plants to release their hold on flower buds at different times. In USDA zones 3 through 9, daylily sepals (Hemerocallis spp.) respond to darkness by unfurling at midnight, while four o’clocks (Mirabilis jalapa), which grow in USDA zones 7a through 10b, open late in the afternoon.

Lookalikes

• The sepals of daylilies and Lenten rose (Helleborus orientalis), which are called tepals, are indistinguishable from the flower petals. These tepals assist the petals by giving the flowers an extra burst of color to attract pollinators. Lenten rose flowers have two pollination challenges that their tepals help overcome. Because Lenten rose blooms in USDA zones 4 through 9 during cold-weather months when fewer pollinators are available, the colorful tepals attract insects. The flowers nod, hanging downward, but many tepals are colored on both sides for greater visibility to more pollinators.