Leaf form evolution in Viburnum parallels variation within individual plants

Few studies have critically evaluated how morphological variation within individual organisms corresponds to variation within and among species. Sub-individual variation in plants facilitates such studies because their indeterminate, modular growth generates multiple serially homologous structures along growing axes. Focusing on leaf form, we evaluate how sub-individual trait variation relates to leaf evolution across Viburnum, a clade of woody angiosperms. In Viburnum we infer multiple independent origins of wide/lobed leaves with toothed margins from ancestors with elliptical, smooth-margined leaves. We document leaf variation along the branches of individual plants of 28 species and among populations across the wide range of V. dentatum. We conclude that when novel leaf forms evolved in Viburnum, they were intercalated at the beginning of the seasonal leaf sequence, which then generated a repeated spectrum of leaf forms along each branch (seasonal heteroblasty). We hypothesize that t...