Pollination biology of the endangered Blowout Penstemon (Penstemon haydenii S. Wats.: Scrophulariaceae) in Nebraska1

Abstract

We studied the breeding system and pollinators of Nebraska populations of the endangered plant Blowout penstemon, Penstemon haydenii. This species appears to be one of the few known self-incompatible species of Penstemon few self-pollinated flowers set fruit and few of these produced seeds. We found no indication that sexual reproduction was limited by inadequate pollination or resources. Pollinators were several species of native bees which varied from population to population and from year to year; there did not appear to be a consistent P. haydenii pollinator fauna. Flowers were pollinated mainly by large apid bees in the genera Habropoda and Bombus, by (mostly) smaller halictid bees, and by intermediate sized megachilid bees, particularly in the genus Osmia. One frequent flower-visitor, the presumed Penstemon specialist, Hoplitis pilosifrons (Megachilidae), may be more of a pollen-parasite than a pollinator because it commonly collected pollen into the scopa but carried very little pollen on other body parts. Management plans for conservation of Penstemon haydenii need to recognize its need for pollinators, and that the health of pollinator populations may be site-specific.