The anatomical determinants of leaf hydraulic function

Leaves are enormously diverse in size and shape, and especially in their internal anatomy, including their venation architecture. This variation across species in vein and lamina anatomy carries extensive information about the physiological function, development, evolution, ecology, and paleohistory of leaves. Much of the functional importance of the leaf’s anatomy relates to its role within the plant water transport system. We review the contribution of the anatomy of both the vein system and the outside vein system to the leaf hydraulic conductance (K leaf) and to K leaf dynamics with leaf water status, in particular reviewing the role of vein xylem traits, bundle sheath and bundle sheath extensions, and lamina tissues. We show that K leaf and its vulnerability depend on multiple anatomical traits in concert, at levels of tissue and organ construction. We further highlight the reasons that such trait correlations arise, i.e., due to mechanistic linkages, coselection, and/or common development. We review recent understanding of the anatomical integration of the leaf hydraulic and gas exchange systems. Finally, we summarize the current and future approaches that will continue to reveal the anatomical underpinnings of K leaf at higher resolution with certain benefits for predictive ecology and for optimal crop design.