Cover Story: C₂ photosynthesis is often associated with C₃-C₄ evolutionary intermediate species, as an intermediate physiological state between the ancestral C₃ and derived C₄ photosynthetic types. Here we review the role of C₂ phenotypes across scales – from biochemistry to leaf anatomy to gas exchange and biogeography- in the context of C₂ species being C₃-C₄ evolutionary intermediates, but also as evolutionary stable state and C₃ × C₄ hybrid species in an effort to explain the diversity of C₂ phenotypes observed in the literature. View the paper.