Abstract
Leaf shape is closely related to economics of leaf support and leaf functions, including light interception, water use, and CO2 uptake, so correct quantification of leaf shape is helpful for studies of leaf structure/function relationships. There are some extant indices for quantifying leaf shape, including the leaf width/length ratio (W/L), leaf shape fractal dimension (FD), leaf dissection index, leaf roundness index, standardized bilateral symmetrical index, etc. W/L ratio is the simplest to calculate, and recent studies have shown the importance of the W/L ratio in explaining the scaling exponent of leaf dry mass vs. leaf surface area and that of leaf surface area vs. leaf length. Nevertheless, whether the W/L ratio could reflect sufficient geometrical information of leaf shape has been not tested. The FD might be the most accurate measure for the complexity of leaf shape because it can characterize the extent of the self-similarity and other planar geometrical features of leaf shape. However, it is unknown how strongly different indices of leaf shape complexity correlate with each other, especially whether W/L ratio and FD are highly correlated. In this study, the leaves of nine Magnoliaceae species (>140 leaves for each species) were chosen for the study. We calculated the FD value for each leaf using the box-counting approach, and measured leaf fresh mass, surface area, perimeter, length, and width. We found that FD is significantly correlated to the W/L ratio and leaf length. However, the correlation between FD and the W/L ratio was far stronger than that between FD and leaf length for each of the nine species. There were no strong correlations between FD and other leaf characteristics, including leaf area, ratio of leaf perimeter to area, fresh mass, ratio of leaf fresh mass to area, and leaf roundness index. Given the strong correlation between FD and W/L, we suggest that the simpler index, W/L ratio, can provide sufficient information of leaf shape for similarly-shaped leaves. Future studies are needed to characterize the relationships among FD and W/L in leaves with strongly varying shape, e.g., in highly dissected leaves.
Highlights
Leaf shape can be represented by the ratio of leaf width to length for many higher plants, and it shows a correlation with the geometric characteristics of leaf venation network
We studied nine Magnoliaceae species with typical reticulate leaf venation to determine if correlations between leaf indices related to leaf shape and size and leaf shape fractal dimension (FD) hold true
There were significant differences in the leaf W/L ratios among the nine Magnoliaceae species (Figure 4A), and similar differences were found for the calculated FD values (Figure 4B)
Summary
Higher plants usually have a hierarchical leaf venation network and broad leaves. Leaf shapes of eudicots exhibit a high degree of complexity, and the shape complexity is associated with leaf venation patterns [1]. Leaf venation architecture is further intimately associated with leaf hydraulics and water supply [2]. Parallel vein patterns with stomata distributed linearly in intercostal areas along the veins are found in Poaceae plants, while hierarchical reticulate venation network with regular or homogenous Poisson random stomatal distribution are found in many eudicots. The hierarchical reticulate venation is considered as an evolutionary “innovation” [3], because it reduces hydraulic transport distance from leaf veins to stomata and water resistance through mesophyll cells [4]. The hierarchical reticular venation can support wider leaves, and the mesophyll cells may be farther away from the midrib due to the advanced leaf venation network
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
