The role of resources and architecture in modeling floral variability for the monoecious amphicarpic Emex spinosa (Polygonaceae)

Determining the sources of floral variation is crucial to the understanding of floral evolution. Architectural effects and phenotypic plasticity in development can play an important role in intraplant floral variation, giving rise to gender dimorphism or sexual specialization. Amphicarpic plants have another source of floral variation that could also be influenced by positional effects. We studied the effects of resource availability and architecture in intraplant floral variability in two ecotypes of the amphicarpic Emex spinosa. Male flowers were smaller than females, irrespective of position or resource availability. Emex spinosa shows gender dimorphism not influenced by positional effects. Flower size differences among positions were mainly due to architecture, because the effects of resources on flower size were minimal. Architectural effects caused a decrease in female flower size from ground to apical positions but an increase in most male traits that resulted in sexual specialization at the end of flowering. In general, the ecotypes were similarly affected by resources or architecture. Differences between subterranean and aerial female flowers seem also to be a consequence of architecture. Our results contribute to the evidence that resource limitation is an overestimated effect and that architectural effects must be considered in studies of floral or fruit variation.