Valiente-Banuet A., Molina-Freaner F., Torres A., Arizmendi M. C., Casas A., Geographic differentiation in the pollination system of the columnar cactus Pachycereus pecten-aboriginum, American Journal of Botany, 2004, 91(6):850-855, doi: 10.3732/ajb.91.6.850
A comparison of Pachycereus pecten-aboriginum flowering on tropical Pajarera Island and in northern Sonora documents geographic variation in pollination. Visitor exclusion experiments accompany measurements of flower opening and nectar secretion. Both populations are self-incompatible, but differ in the contribution of daytime and nighttime pollinators.