We provide a dataset documenting the changes in male and female morphological traits after evolution at low- and high-density during three generations in the dioecious plant species Mercurialis annua. Our dataset corresponds to results from an experimental evolution protocol in which we have measured male and female traits after the evolution of ten experimental independent populations at the two contrasting densities. Seeds were initially collected in various populations of the species range and grown for three generations in a common garden, which aim was to build a seed bank with large genetic variance for experimental evolution. The seeds resulting from this initial generation (G0) have than been grown to build ten experimental populations (POP in the dataset) that were affected either to low or high density (TREAT in the dataset). Each population was grown separately from the other populations and its assigned density was applied during the last four weeks of growth. After three generations of evolution at their assigned density, seeds resulting from the third generation of evolution were grown in a common garden with two spatial blocks (BLOCK in the dataset) in which we recorded the spatial position of each plants (x and y in the dataset) measured vegetative and reproductive traits in male and female plants.

A README file is provided as well as a description of the dataset directly within the datafile.