Leaf vascular systems in C3 and C4 grasses:: A two-dimensional analysis

center dot Background and Aims It is well documented that C-4 grasses have a shorter distance between longitudinal veins in the leaves than C-3 grasses. In grass leaves, however, veins with different structures and functions are differentiated: large longitudinal veins, small longitudinal veins and transverse veins. Thus, the densities of the three types of vein in leaves of C-3 and C-4 grasses were investigated from a two-dimensional perspective. center dot Methods Vein densities in cleared leaves of 15 C-3 and 26 C-4 grasses representing different taxonomic groups and photosynthetic subtypes were analysed. center dot Key Results The C-4 grasses had denser transverse veins and denser small longitudinal veins than the C-3 grasses (1.9 and 2.1 times in interveinal distance), but there was no significant difference in large longitudinal veins. The total length of the three vein types per unit area in the C-4 grasses was 2.1 times that in the C-3 grasses. The ratio of transverse vein length to total vein length was 14.3 % in C-3 grasses and 9.9 % in C-4 grasses. The C-3 grasses generally had greater species variation in the vascular distances than the C-4 grasses. The bambusoid and panicoid C-3 grasses tended to have a denser vascular system than the festucoid C-3 grasses. There were no significant differences in the interveinal distances of the three vein types between C-4 subtypes, although the NADP-malic enzyme grasses tended to have a shorter distance between small longitudinal veins than the NAD-malic enzyme and phosphoenolpyruvate carboxykinase grasses. center dot Conclusions It seems that C-4 grasses have structurally a superior photosynthate translocation and water distribution system by developing denser networks of small longitudinal and transverse veins, while keeping a constant density of large longitudinal veins. The bambusoid and panicoid C-3 grasses have a vascular system that is more similar to that in C-4 grasses than to that in the festucoid C-3 grasses.