What is a plant spur?

In botany, a spur is a hollow, nectar-producing outgrowth from the base of a flower, such as the one found in the genera Aquilegia, Tropaeolum, Delphinium, Viola and Impatiens. Spurs also occur in some genera of orchids. Nectaries that are localized in spurs present a foraging challenge to pollinators; only those with mouthparts or tongues long enough to reach the nectar at the base of the spur can exploit these food rewards. The length and shape of the spur and its corresponding pollinator's mouthparts have co-evolved. Nectar spurs are often associated with the pollination of long-tongued bees and butterflies, hummingbirds, and hawkmoths.

Some plants have modified their floral spurs to trap pollinating insects. For example, the flowers of the common snapdragon (Antirrhinum majus) have a lower petal modified to form a spring-loaded trap that ejects trapped pollinators covered with pollen. Certain species of orchids have spurs which act like pitfall traps, trapping ants which serve as pollinators for the flowers.