Fig. 3.

Plants have evolved various mechanisms to control the rate of pollen presentation to plants. Plants may stagger the opening of flowers or anthers within flowers to control the amount of pollen exposed to individual pollinators. (A) For example, the anthers of some species (e.g. Lillium longiflorum) expose pollen quickly so that large vector pollen loads are placed onto vectors with each visit. Other species expose their pollen over the course of many days so that pollen is placed onto vectors in small doses through multiple visits. Here, we show the slow release of Gethyllis verticillata pollen as the anthers roll up and dehisce over several days: (B) day 1, (C) day 3. Photos: B. Anderson. (D) Although pollen from Asclepias verticillata is aggregated in pollinia and presented to pollen vectors all at once, the rate of pollen removal may be controlled by the low probability of the pollinarium’s corpusculum attaching to a pollinator. This can be influenced by floral features such as floral structure or nectar abundance which impact visit duration. Each pollinarium comprises joined pollinaria from adjacent anthers (there are five anthers in Asclepias), and the attachment of a single pollinarium to the hairs or bristles of visiting pollinators removes one-fifth of the flower’s pollen in a single visit. Note the paired pollinaria (indicated by an arrow in D) on the left front leg of the bee Bombus griseocollis, magnified in (E). Photos: J. Karron.