The stigma and stamen are enclosed in the sheath of the keel petal. The pressure of a bee visiting the flower squeezes out a string of pollen from the opening in the keel petal. When the pressure is removed, the tips of the anthers return to their former position, and, when pressure is renewed, fresh pollen masses are extruded. At a later stage, the stigma elongates and also projects through the cleft. After the pollen is carried away or no longer viable, the stigma becomes receptive to pollen brought from other flowers.
Bees are primary pollinators of kidneyvetch.