Aguilar-García S. A., Figueroa-Castro D. M., Valverde P. L., Vite F., Effect of flower orientation on the male and female traits of Myrtillocactus geometrizans (Cactaceae), Plant Biology, 2018, 20(3):531-536, doi: 10.1111/plb.12713
North-facing and south-facing flowers were compared in a population from the Tehuacán Valley. Orientation was associated with differences in most traits examined, including pollen production and some measures of pollen quality. Southern flowers had more anthers, among other differences, and their pollen germinated better in laboratory conditions. Greater resource availability under higher illumination remains a proposed mechanism for these associations.