The number of lips a flower has depends on its specialized anatomy. The term “lips” refers to highly modified and often fused petals found in particular plant families, structures that have evolved to resemble mouths. While many flowers have a circular array of petals, certain species feature a division of their petals into distinct upper and lower sections. This unique arrangement is an adaptation where the flower’s form prioritizes precise, functional design over symmetrical beauty.
The Botanical Basics of Flower Structure
The typical flower structure involves the calyx (sepals) and the corolla (petals). Many common flowers exhibit radial symmetry, meaning they can be divided into identical halves along multiple planes, such as daisies and buttercups.
Flowers that develop “lips” belong to a group defined by bilateral symmetry, which means they can only be divided into two mirror-image halves along a single plane, much like a human face. This change from a radial to a bilateral design is a fundamental evolutionary shift. This specific symmetry gives rise to specialized structures, enabling the petals to fuse and differentiate into distinct, asymmetrical forms.
Defining the Floral Lips
Floral lips are specialized petals that have fused and elaborated into distinctive shapes. In the orchid family, one of the three petals is modified into a large, prominent structure called the labellum, or lip. This median petal is the most visually complex part of the orchid flower, often differing significantly in size, color, and texture from the other petals and sepals.
Flowers in the mint family (Lamiaceae) commonly display two lips, an upper and a lower. The corolla is typically divided into two distinct parts: the upper lip is formed from the fusion of two petals, and the lower lip is formed by the fusion of the remaining three petals. This arrangement creates a tubular opening with two clear, opposing structures.
Why Flowers Develop Lips
The development of these floral lips is a result of co-evolution, driven by the need for efficient and specific pollination. The lips function as a precise mechanism to control the interaction between the flower and its pollinator. The lower lip or labellum often acts as a specialized landing platform, providing a secure spot for an insect to stand while accessing the flower’s nectar.
This landing platform guides the pollinator into a specific position, ensuring the insect’s body contacts the anthers (pollen-bearing structures) and the stigma (pollen-receiving structure). The shape and dimension of the lip often correspond exactly to the size and shape of a particular pollinator, making the pollination process highly specialized. Some orchid lips even feature fleshy lumps, known as calli, or intricate color patterns that serve as visual guides to direct the pollinator toward the reproductive organs.
Examples of Lip-Bearing Flowers
Striking examples of floral lips are found across several diverse plant families. In the orchid family, the labellum is a versatile structure that often uses mimicry to attract pollinators. Some orchid labella resemble female insects and produce chemical signals to attract male pollinators for a deceptive mating attempt.
The two-lipped structure is common in the mint family, which includes culinary herbs like sage and mint. These flowers have a prominent lower lip that serves as a platform, while the upper lip arches over the top, sheltering the reproductive parts and ensuring that a visiting bee is dusted with pollen as it enters the tubular corolla. Snapdragons (Antirrhinum) also feature bilaterally symmetrical flowers. Their lower lip must be depressed by a heavy insect to allow access to the nectar and pollen within.