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).