# GC-MS Analysis of the Volatile Constituents in the Leaves of 14 Composite Plants
## 2 Results
### PCA Analysis of 14 Composite Plants Based on terpenoid Compounds  
Considering that terpenoid compounds were the predominant components in the tested species, the terpenoid concentrations in the 14 samples were subjected to principal component analysis (PCA) for a better description of these scented plants. Five principal components were obtained, and the accumulated variance of PC1, PC2, PC3, PC4, and PC5 accounted for 71.73%, 64.31%, 56.70%, 46.52%, and 26.23% of the total variance, respectively. Therefore, the first two principal components were chosen to construct a loading diagram. According to the factor scores, the tested samples were positioned in the two-dimensional space, with some obvious groupings (Figure 4A). These  
Figure 3: Relative content of volatile constituents in the leaves of 14 samples. Sample numbers are the same as in Table 2. MT, monoterpenes; ST, sesquiterpenes; DT, diterpenes; OT, oxygenated terpenes; AC, aromatic compounds; FC, fluorinated compounds; TC, total compounds. groups could be well explained based on the loading spots of the terpenoid components (Figure 4B). The group consisting of _C. indicium_ var. _aromatic_ (**S10**), _C. indicium_ (**S11**), _O. longilobus_ (**S13**), and _O. tailangensis_ (**S14**), with the highest PC1 scores and negative PC2 scores, were characterized by high amounts of \(\alpha\)-thujone, which accounted for 1432.16 ng/g FW, 552.64 ng/g FW, 283.73 ng/g FW, and 531.48 ng/g FW, respectively. Germacrene D (a sesquiterpene) was the most abundant component of the total terpenids in the leaves of _A. sacorum_ (**S1**), _A. japonica_ (**S5**) and _C. chinense_ (**S12**), accounting for 260.91 ng/g FW (31.77%), 77.36 ng/g FW (28.10%), and 80.42 ng/g FW (14.70%), respectively, and grouped these species together with high PC1 and PC2 scores. Close to these three species, _T. vulgare_ (**S9**), whose major component was camphor (317.22 ng/g FW, 27.34%), also contained a high percentage of germacrene D (126.68 ng/g FW, 10.92%), followed by \(\beta\)-phellandrene (85.13 ng/g FW, 7.34%), eucalypt (45.36 ng/g FW, 3.91%) and \(\beta\)-ylangene (40.89 ng/g FW, 3.52%), in its leaves. Another group consisted of _A. vulgaris_ 'Variegate' (**S3**) and _A. argyi_ (**S8**), which were characterized by high concentrations of \(\beta\)-caryophyllene. _A. vulgaris_ 'Variegate' (**S3**) contained \(\beta\)-caryophyllene (181.14 ng/g FW, 17.35%) as the major terpenoid, followed by \(\beta\)-pinene (62.92 ng/g FW, 6.03%) and _trans_-\(\beta\)-farnesene (59.17 ng/g FW, 5.67%). Similarly, the most abundant terpenids in the leaves of _A. argyi_ (**S8**) included \(\beta\)-caryophyllene (258.69 ng/g FW, 12.40%), eucalypt (343.57 ng/g FW, 16.47%), and artemisinin ketone (293.39 ng/g FW, 14.06%). Eucalyptust (157.46 ng/g FW, 9.93%) was also a main terpenoid constituent in the leaves of _A. abrotanum_ (**S6**), which also contained silphiperfol-5-en-3-one A (346.20 ng/g FW, 21.84%), 6-camphenol (140.13 ng/g FW, 8.84%), and cedrol (113.80 ng/g FW, 7.18%) as its main components. Three samples were located at positions near the original point but had different terpenoid compositions and concentrations (Figure 4A). Among them, _A. absinthium_ (**S2**) contained \(\alpha\)-phellandrene (175.54 ng/g FW, 20.97%) and \(\beta\)-phellandrene (150.17 ng/g FW, 17.94%) as the predominant compounds. Many terpenids such as germacrene D, \(\beta\)-phellandrene, arborescin, and \(\beta\)-caryophyllene in the leaves of _A. yunnensis_ (**S4**) were present at high concentrations that exceeded 150 ng/g FW, but the concentration of arglobin (2830.67 ng/g FW, 47.72%) was higher than the concentrations of all other compounds in this sample. The leaf extract of _A. sericea_ (**S7**) possessed abundant _trans_-chrysanthenyl acetate (303.35 ng/g FW, 34.87%) and relatively low concentrations of other terpenoid components, such as _cis_-verbenol (31.05 ng/g FW, 3.57%), safranal (13.17 ng/g FW, 1.51%), and tetrahydromyrcenol (4.29 ng/g FW, 0.49%).