Early life-history stages of cacti can benefit from the facilitative effects of nurse plants that reduce solar radiation and water stress. Miranda-Jácome et al. conduct a reciprocal transplant experiment, coupled with the artificial manipulation of sun/shade conditions, to test for the effects of local adaptation on germination, seedling survival and growth of the columnar cactus Pilosocereus leucocephalus. They find that significant local adaptation is mainly detected under full sunlight conditions, indicating that sun/shade acts as a selective agent in water-limited environments. Facilitation provided by nurse plants in these environments can attenuate the patterns of local adaptation among plants benefiting from nurse plant effects.