Hummingbird and bee pollination of Penstemon pseudospectabilis

We studied the pollination effectiveness of hummingbirds and bees, and the breeding system and nectar production rate of Penstemon pseudospectabilis M . E. Jones in the Chiricahua Mountains, Arizona. With pink rather than red flowers, a corolla tube as long as a hummingbird bill but wide enough to ad mit bees, and hummingbird-typical nectar sugar composition, P. pseudospecta bilis may be adapted for pollination by both hummingbirds and bees. Manual outcrossing yielded more than twice as many seeds/flower as manual selfing. When all visitors were excluded most plants produced some seeds through au tonomous self-pollination (7/flower), but seed set increased more than two- fold when flowers were manually selfed. Flowers visited only by small, main ly halictid bees had seed set similar to the hand-self treatment (significa ntly better than no visits), whereas those visited mainly by hummingbirds a nd honeybees had seed set comparable to the hand-outcrossed treatment. The daily nectar production rate of 3.96 mg sugar/flower was relatively high fo r hummingbird flowers of the western United States (typical range: 2-4 mg s ugar/flower), rather than being intermediate between hummingbird and bee fl owers. Hummingbirds visited an observation patch at least hourly. Our resul ts support a previous conclusion about a "mixed pollination system" in this species, and provide an example of a Penstemon species which is significan tly self-incompatible and attracts high-energy pollinators (hummingbirds), but retains the ability to self-pollinate and profit from small bee visitor s.