Flowers play a crucial role in plant reproduction by attracting organisms like insects and birds to transfer pollen. This attraction often relies on providing a reward, encouraging interaction with the flower’s reproductive structures.
Understanding Nectar
Nectar is a sugary liquid produced by plants to attract pollinators. It mainly consists of sugars like sucrose, glucose, and fructose, providing an energy source for visiting animals. Nectar also contains amino acids, ions, and vitamins, contributing to its nutritional value. This sweet secretion guides animals to engage with the flower, facilitating the plant’s reproductive success through pollination.
The Nectary Structure
Nectar is found within specialized glandular structures called nectaries. These nectaries are composed of modified epidermal cells, supported by vascular bundles that supply resources. Nectaries exhibit diverse locations within a flower, depending on the plant species and its pollinator. They can be at the base of petals, such as in buttercups, or on sepals, stamens, or the ovary, often as a disc surrounding the pistil. Their placement ensures a pollinator contacts the flower’s reproductive parts while accessing nectar.
Nectar Production and Secretion
Nectar production and secretion occur within nectary cells. Sugars, primarily sucrose, are transported to the nectary through the phloem. In the nectary cells, sucrose is often broken down into glucose and fructose, then actively released onto the surface. This active transport allows the plant to control the nectar’s concentration and volume. This process ensures a consistent supply of this sugary reward to attract and retain pollinators.
Diverse Nectar Locations
Nectar placement varies across plant species, adapting to specific pollinators. In some flowers, nectaries are openly accessible, such as the disc-shaped nectaries in the carrot family, allowing a wide range of short-tongued insects to feed. Other flowers, like columbines, have nectaries at the end of long, slender spurs, restricting access to pollinators with specialized mouthparts, such as hummingbirds or long-tongued moths. This diversity ensures the plant attracts efficient pollinators for its reproductive strategy.
Columbine flowers (Aquilegia) feature five distinct, long, hollow spurs that project from the rear of the petals, with nectar gathered at their tips. This specific arrangement means that only pollinators with sufficiently long tongues, such as hummingbirds or certain long-tongued insects like hawkmoths, can access the nectar effectively. The evolution of these spur lengths in columbines has been shown to match the tongue lengths of their primary pollinators, illustrating a close co-evolutionary relationship. This specialization ensures efficient pollination by guiding the pollinator directly to the reproductive parts of the flower while it feeds.