Fig. 1

A general model of leaf length and half-leaf width quadratic relationship, taken one C. lanceolata leaf as an example here (more details are shown in supporting information Fig. S1). The leaf width of needles universally ranges from 0.04 to 0.15 cm, while broad leaves perform much wider (greater than 1 cm) [37, 38]. Further, the modeled species C. lanceolata show somewhere in between. The images on the top, middle, below are the half-leaf width model, the contour extraction image and the original scanned image, separately. The data of the model come from the middle image, and blue line means leaf length between leaf petiole to tip along leaf midrib, red lines mean leaf widths at every 0.1 cm length segments. Green dots in the model represent half-leaf width marginal hydraulic possibility, and dark linear shows the leaf tapering function between half-leaf width(Y) and leaf length(X), which could be fitted as: Y = C + B₁X + B₂X². Diameters are shown in below image