Hummingbird and bee pollination of Penstemon pseudospectabilis

• Published in: The journal of the Torrey Botanical Society 1999-04, Vol.126 (2), p.99-106
• Main Authors: Lange, R.S, Scott, P.E
• Format: Article
• Language: English
• Subjects: Bumblebees; Flowers; Honey bees; Hummingbirds; Insect pollination; Nectar; Penstemon; Penstemon pseudospectabilis; Plants; Pollinating insects; Pollination; pollinators; Seed set
• ISSN: 1095-5674; 1940-0616
• DOI: 10.2307/2997285

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 admit bees, and hummingbird-typical nectar sugar composition, P. pseudospectabilis 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 autonomous self-pollination (7/flower), but seed set increased more than two-fold when flowers were manually selfed Flowers visited only by small, mainly halictid bees had seed set similar to the hand-self treatment (significantly better than no visits), whereas those visited mainly by hummingbirds and honeybees had seed set comparable to the hand-outcrossed treatment The daily nectar production rate of 3 96 mg sugar/flower was relatively high for hummingbird flowers of the western United States (typical range: 2-4 mg sugar/flower), rather than being intermediate between hummingbird and bee flowers Hummingbirds visited an observation patch at least hourly Our results support a previous conclusion about a "mixed pollination system" in this species, and provide an example of a Penstemon species which is significantly self-incompatible and attracts high-energy pollinators (hummingbirds), but retains the ability to self-pollinate and profit from small bee visitors.