Figure Legend
Figure 1 . Spatial distribution of the data in this study. Each dot represents a species’ central distribution location in China, using the mid-latitude and mid-longitude values of the species’ range in the country as coordinates.
Figure 2 . Frequency distribution of five tracheid traits for 79 conifer species. Blue bars stand for earlywood and red bars for latewood.
Figure 3 . Phylogenetic PCA of earlywood and latewood characters for 79 conifer species from five families. Acronyms for tracheid traits are listed in Table 1. Trait names followed by ‘s’ stand for earlywood while ‘a’ is for latewood.
Figure 4 . Phylogenetic PCs of earlywood and latewood traits along the phylogenetic tree. Bubbles stand for Moran’ values for each species along the phylotree with a legend at the bottom-left. The node-1 label is added to emphasize two clades of the phylotree: Pinaceae species in the upper part of the phylotree generally showed negative values, suggesting there are more frequent divergences in traits related with PC1. On the contrary, Cupressaceae species and others in the lower branches showed positive values, suggesting xylem traits related with PC1 of the species were conserved.
Figure 5 . Interspecific variation in tracheid characters along a latitudinal gradient taking phylogeny into account. R2 stands for the explanatory power of the climatic variable in PGLS models, subscript “s” in R2 stands for earlywood, while “a” stands for latewood. Blue and red lines stand for fitted GPLS models for earlywood and latewood data, respectively.