## 2 Results and Discussion
### Fingerprints of Selaginella doederleinii  
Under the optimum extraction conditions, HS-SPME-GC-MS was used to identify the volatile oil of SD samples from Guizhou and Zhejiang provinces. The experiment was repeated three times. The total peak area, RI, and relative percentage content of the volatile oils from the herbs were calculated [25]. The total ion chromatogram (TIC) of SD from different origins are shown in Figure 2. As shown in Tables 1 and 2, a total of 58 volatile compounds, including 20 terpen, 11 alkanes, 3 alcohols, 6 ketones, 3 esters, 11 aldehydes, 1 ethers, 1 aromatic, 1 phenol, and 1 furan were found and identified in SD. Among them, 45 volatile components were reported in the volatile oils of SD for the first time. The concentration of each component differed among the volatile oils from 24 habitats of SD. For instance, the concentration of anethol in the volatiles of SD from Guizhou was over 20 times higher than that in the volatile oils of SD from Zhejiang. Consequently, in order to find the marker \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Compound Type**} & \multirow{2}{*}{**Numbers**} & \multicolumn{2}{c}{**Peak Areas Ratios (\%)**} \\ \cline{3-4}  & & **Zhejiang (\(n\) = 11)** & **Guizhou(\(n\) = 13)** \\ \hline aldehyde & 11 & 11.27 \(\pm\) 0.55 & 16.30 \(\pm\) 0.57 \\ alcohol & 3 & 0.53 \(\pm\) 0.23 & 1.61 \(\pm\) 0.13 \\ ketone & 6 & 14.93 \(\pm\) 0.68 & 11.61 \(\pm\) 0.46 \\ furan & 1 & 7.50 \(\pm\) 0.52 & 5.48 \(\pm\) 0.34 \\ alkane & 11 & 12.65 \(\pm\) 1.12 & 16.42 \(\pm\) 0.67 \\ ether & 1 & 0.31 \(\pm\) 0.06 & 0.73 \(\pm\) 0.16 \\ phenol & 1 & 1.38 \(\pm\) 0.12 & 0.42 \(\pm\) 0.07 \\ terpene & 20 & 45.00 \(\pm\) 3.14 & 43.77 \(\pm\) 2.16 \\ aromatic & 1 & 0.37 \(\pm\) 0.08 & 0.43 \(\pm\) 0.07 \\ ester & 3 & 3.29 \(\pm\) 0.48 & 2.79 \(\pm\) 0.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Different compound categories in _Selaginella doederleinii_ from 24 habitats. Figure 2: Typical chromatogram of the volatile components from _Selaginella doederleinii_ by headspace solid phase microextraction and gas chromatography-mass spectrometry (HS-SPME/ GC–MS). compounds for the comparison of SD Guizhou and SD Zhejiang, an unpaired T-test was employed for analyzing the relative contents of the common peaks of SD [26]. As shown in Figure 2 and Table 2, there were significant differences in volatile components between them. The main components of SD from Guizhou included: Anethol (12.78 \(\pm\) 0.31%), cedrol (6.97 \(\pm\) 0.18%), 2,4-nonadienal (5.60 \(\pm\) 0.34%), 2-pentylfuran (5.48 \(\pm\) 0.13%), phytone (5.44 \(\pm\) 0.24%), hexadecane (3.19 \(\pm\) 0.39%), linalool (3.36 \(\pm\) 0.23%), and aromadendrene (3.70 \(\pm\) 0.15%). The main components of SD from Zhejiang included: Phytone (11.41 \(\pm\) 1.21%), 2-pentylfuran (7.50 \(\pm\) 0.52%), carvacrol (2.21 \(\pm\) 0.48%), ledene (5.48 \(\pm\) 0.13%), cedrol (4.66 \(\pm\) 0.79%), 2,4-nonadienal (4.65 \(\pm\) 0.76%), aromadendrene (4.80 \(\pm\) 0.56%), \(\beta\)-caryophyllene (2.54 \(\pm\) 0.19%), zingerone (5.84 \(\pm\) 0.59%), and n-hexadecane (3.61 \(\pm\) 0.43%). Among the above presented components, the relative contents of phytone, cedrol, aromadendrene, hexadecane, and 2-pentylfuran were more than 3% in all SD samples. In general, the contents of aldehydes, alcohols, alkanes, ethers, and aromatics in SD from Guizhou Province were higher than those from Zhejiang Province (Table 1). It was worth noting that the difference among aldehydes was particularly significant. The aldehydes in Zhejiang and Guizhou accounted for 11.27 \(\pm\) 0.55% and 16.30 \(\pm\) 0.57%, respectively, including 2-heptenal, 2-octenal, 1-nonanal, 2-nonenal, decanal, 2,4-nonadienal, citral, 2,4-decadienal, dodecanal, 2-butyl-2-octenal, and tetradecanal. There was a significant difference in the contents of aldehydes and alkanes between the two regions (\(p<0.05\)).