Abstract: The phenotypic plasticity of plants has been explored as a function of either ontogeny (apparent plasticity) or environment (adaptive plasticity), although few studies have analyzed these factors together. In the present study, we take advantage of the dispersal of Aechmea mertensii bromeliads by Camponotus femoratus or Pachycondyla goeldii ants in shaded and sunny environments, respectively, to quantify ontogenetic changes in morphological, foliar, and functional traits, and to analyze ontogenetic and ant species effects on 14 traits. Most of the morphological (plant height, number of leaves), foliar (leaf thickness, leaf mass area, total water content, trichome density), and functional (leaf δ13C) traits differed as a function of ontogeny. Conversely, only leaf δ15N showed an adaptive phenotypic plasticity. On the other hand, plant width, tank width, longest leaf length, stomatal density, and leaf C concentration showed an adaptation to local environment with ontogeny. The exception was leaf N concentration, which showed no trend at all. Aechmea mertensii did not show an abrupt morphological modification such as in heteroblastic bromeliads, although it was characterized by strong, size-related functional modifications for CO2 acquisition. The adaptive phenotypic variation found between the two ant species indicates the spatially conditioned plasticity of A. mertensii in the context of insect-assisted dispersal. However, ant-mediated effects on phenotypic plasticity in A. mertensii are not obvious because ant species and light environment are confounding variables. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 299–312.