Bringing anatomy back into the equation

There is more than metaphorical appeal to the thought that humanity feeds off the sweat of vascular plants. This statement has factual grounds in the sense that plant water loss by transpiration is an inevitable companion to the photosynthetic process that nourishes the human population. A fascinating corollary of this linkage between water and carbon is that leaf productivity in well-watered plants is constrained by the efficiency with which the plant vascular system can deliver water to the sites of photosynthetic gas exchange in leaves. Plant history shows us that species with a high capacity for transporting water have prevailed over less efficient predecessors (Raven, 1977), and this trajectory is particularly evident in studies of the evolution of angiosperm leaf vascular systems (Boyce et al., 2009).