Population-wide estimates of outcrossing rates were surprisingly low for a species with showy, entomophilous flowers and ranged from 1.9% in an experimental population with a "clumped' spatial arrangement to 8.5% in an experimental population with a "dispersed' arrangement. For individual plants and single flowers in the experimental populations, variation in outcrossing rates was significantly affected by such population-wide characteristics as plant spatial arrangement and nightly fluctuations in total floral abundance, but by far the most important factor was stigma position. Flowers with stigmas above the anthers had significantly higher outcrossing rates than did flowers with overlapping stigma and anthers. The very low population-wide levels of outcrossing may represent a persistent mixing mating system rather than a transition to complete selfing. -from Authors