Deep flowers are characterized by their elongated, tubular, or trumpet-like floral structures. The flower’s form creates a floral tube that effectively holds nectar deep within. This design makes it accessible only to certain visitors, playing a direct role in its reproductive process.
The Co-evolutionary Partnership
The existence of deep flowers is a result of co-evolution, where two or more species reciprocally affect each other’s evolution. This relationship is like a “lock and key” mechanism. The deep flower is a specialized lock, while the pollinator’s feeding anatomy is the matched key, ensuring only specific animals can access the nectar.
This arrangement benefits both partners. The plant gains a dedicated pollinator, leading to more reliable pollen transfer. For the pollinator, the deep flower represents a private food source with less competition. Over millions of years, this mutual reliance has driven the evolution of deeper flowers and longer tongues or beaks in their animal partners.
Specialized Pollinators
A select group of animals has evolved the anatomy to access nectar within deep flowers. Hummingbirds, with their long beaks and tongues, are prime examples, and their ability to hover allows them to probe floral tubes with precision. Certain insects, such as hawkmoths and some butterflies, have a long feeding tube called a proboscis to reach the nectar. Some species of long-tongued bees are also adapted to forage from these blossoms.
The flowers’ characteristics often provide clues about their pollinators. Flowers that rely on hummingbirds are often red or orange but typically lack a strong scent, as birds have a poor sense of smell. Conversely, flowers pollinated by nocturnal hawkmoths are often pale, making them more visible in low light, and are intensely fragrant, releasing their scent in the evening to attract visitors.
Examples in the Garden
Many garden plants showcase this evolutionary strategy. Honeysuckle vines have long, slender tubes suited for the proboscis of a moth or the beak of a hummingbird. The drooping flowers of a fuchsia plant are hummingbird attractors, offering a deep nectar reservoir. Trumpet vine is another example, with large, trumpet-shaped flowers that are a favorite of hummingbirds.
Columbine flowers have spurred petals that hold nectar, catering to hummingbirds and long-tongued insects. The tubular flowers of penstemon are also frequently visited by hummingbirds and certain types of bees. These plants are living examples of the partnership between a flower and its pollinator.