PC1 of tracheid characters differ between families
Different traits showed a different pattern for autocorrelation with phylogeny. All tracheid features except cell wall thickness of earlywood were closely correlated with PC1, which contained 80% of all the information, and the cell wall thickness of earlywood was mainly correlated with PC2, which contained 12% information (Fig. 3). Therefore, PC1 stands for the xylem structure including features of earlywood and latewood in terms of cell diameter, cell length and cell wall thickness. For the two species-rich families, Pinaceae and Cupressaceae, their respective species were at opposite ends along PC1 (Fig.3). Podocarpaceae and Taxaceae also appeared to be positioned at the opposite end of Pinaceae; however, this was hard to confirm due to the limited number of five species of Podocarpaceae and Taxaceae analysed (Fig.3).
According to PC1, the first node on the phylotree divided all species excluding Ginkgo biloba into two groups (Fig. 4). Species from Cupressaceae and other families at the lower part of the phylotree showed some high positive Moran’ values (i.e., global structure), while Pinaceae species were located at the upper part of the phylotree and showed maily negative Moran’ values (i.e., local structure). A positive autocorrelation is the result of similarity in related species at the tips of the phylogeny, especially in Juniperus andCephalotaxus . Negative autocorrelation results from differences among closely related species in the tips of the phylogeny, and was most clear in Larix and Keteleeria . Traits closely related to PC1 diverged more strongly within Pinaceae than in other conifer species along the phylogeny (Fig. 4).