Some flowers use scent to attract pollinators. Scent is a signal that helps pollinators find and select particular flowers. These floral scents are typically a complex mixture of highly volatile compounds and essential oils that flowers emit into the atmosphere. A flower scent's structure, color, and odor are important in attracting pollinators. Flowers can be identical in their color or shape, but no two floral scents are exactly the same because of the diversity of volatile compounds, relative abundances, and interactions.

A pollinator detects a flower's scent and follows the concentration gradient of the chemical producing the scent to the flower. Plant species pollinated by bees and flies have sweet scents and those pollinated by beetles have strong musty, spicy, or fruity odors. Flowers that use scents to attract their pollinators are generally drab in appearance, white or purple-brown to dark red-brown, and exude very strong scents that can be detected at a distances over one kilometer.

Plants' scent levels tend to be highest when the flowers are ready for pollination and when potential pollinators are active. Bees or butterflies pollinate plants whose scent is high during the day, while moths and bats pollinate plants whose fragrance is greatest at night. Newly opened and young flowers, not ready to function as pollen donors, produce fewer odors and are less attractive to pollinators than older flowers. Once a flower has been sufficiently pollinated, changes occur with the floral bouquets that lead to these flowers being less attractive and thereby direct pollinators to unpollinated flowers, maximizing the reproductive success of the plant.

Research that has been conducted in the past several years has shown that greenhouse gases from fossil fuels can decrease the concentration of volatile oils (scent) and the distance at which the scent can still be detected by pollinators. Further research is needed to determine the effects upon flowers being successfully pollinated and the ability of the pollinators to find the nectar and pollen to sustain their populations.

How many times have you been intoxicated by the smell of a flower? Many of the chemicals used in aromatherapy are derived from floral scent chemicals; i.e. essential oils.

The beautiful flowers and spicy scent of roseshell azalea (Rhododendron prinophyllum) are always certain to please. Photo by Penny Stritch.

Birds have no sense of smell. Red flowers that rely on birds for pollination often have no smell, such as scarlet gilia (Ipomopsis aggregata). Photo by Teresa Prendusi.