Sunflowers are significant nectar producers, creating a sugary liquid reward that interacts with the broader ecosystem. Nectar is a water-based solution containing various sugars, secreted by specialized plant glands called nectaries. The common sunflower, Helianthus annuus, is recognized as an abundant source of this sweet substance, making it valuable for agriculture and wild insect populations.
Where Sunflowers Produce Nectar
Sunflowers produce nectar in two distinct locations, each serving a different purpose. The first location is the floral nectaries, situated deep within the flower head at the base of the disk florets, directly above the ovary. This nectar is the primary attractant for pollinators like bees, ensuring the plant’s reproduction and seed set.
The second location is the extrafloral nectaries (EFNs), found outside the flower structure on the leaves, bracts, or stem. The liquid secreted by the EFNs serves a defensive role, not pollination. By secreting this sugary substance, the sunflower recruits predatory insects, such as ants, that consume the nectar and patrol the plant, protecting it from herbivores.
What Makes Up Sunflower Nectar
Sunflower nectar is a solution of water and various sugars, which constitute up to 70% of the substance by weight. The three dominant sugars are sucrose, glucose, and fructose, and their ratio and concentration are highly variable. The optimal sugar concentration for many bees falls within a range of 35% to 65% Brix, though some varieties can reach 71.83% Brix.
Sugar concentration is heavily influenced by environmental factors like air temperature and humidity. High humidity can dilute the nectar, lowering the concentration, while warmer temperatures can cause water to evaporate, increasing it. Trace components like amino acids, minerals, and proteins are also present, providing pollinators with nutrients beyond simple energy.
Nectar’s Role in Pollination and Ecosystems
Floral nectar is a vital energy source for a wide variety of insect species, making sunflowers a highly attractive resource in many ecosystems. Honeybees are particularly drawn to the abundant nectar, converting it into a distinct, light-colored sunflower honey. A single hectare of sunflowers can yield between 20 to 30 kilograms of honey.
This plant-insect relationship is a classic example of mutualism: the plant provides a high-energy food source, and visiting insects inadvertently transfer pollen, ensuring reproductive success. The extrafloral nectar contributes to the broader ecosystem by supporting populations of beneficial insects. By feeding predatory insects, the EFNs indirectly aid in pest control, providing a continuous food source for these defenders.