To ensure effective pollen transfer, constancy in the morphological expression of traits involved in the spatial disunion of pistil and stamen (herkogamy) along successive branching is necessary. Camargo et al. measured within-plant trend variation of herkogamy-related traits expressed in response to variation in nutrient availability of two populations that differ in pollinator abundance.
Both populations differ in flower size and had opposite direction in the within-plant variation observed. With decreasing nutrients, a systematic within-plant trend of reduction in flower size, pistil and herkogamy along flower position, increased the probability of self-fertilization in the population of lower pollinator abundance.
Camargo, I. D., Nattero, J., Careaga, S. A., & Núñez-Farfán, J. (2017). Flower-level developmental plasticity to nutrient availability in Datura stramonium: implications for the mating system. Annals of Botany, 120(4), 603–615. https://doi.org/10.1093/aob/mcx093