• Miller, Russell B.

Aquilegia micrantha occurs in canyons of the Southwestern United States. The pinkish-yellow flowers are nodding or semi-nodding, mildly scented, protandrous, and secrete a concentrated nectar (46% total sugars). Seed set in flowers under pollinator exclosures was 25% compared with 63% for open-pollinated flowers. The most common and effective pollinators of A. micrantha in the upper Crystal River Canyon were nectar-foraging bumblebee queens, Bombus appositus and B. flavifrons, although hummingbirds and hawkmoths also visited the flowers, and hummingbirds are important pollinators at other sites. The absence of nectar-foraging Bombus queens on the red flowers of A. elegantula in the area is probably the result of the narrower spur mouths of A. elegantula that prevent the bees from inserting their heads deeply enough into the flowers to extract the nectar. This mechanical isolation may be important in restricting hybridization between the two species in the narrow elevational range of sympatry.