## 3 Results
### Phytochemical Analysis
coriacea_ with (Z)-butyric acid-3-hexenyl ester metabolite dominating with a relative percentage of 29.36% (Table 2). Based on principal component analysis (PCA), the score plot separated the metabolites composition trends between the three species (Supplementary S1). It was found that _H. coriacea_ differed far from _H. cagayanensis_ and _H. lacunosa_ with a total PC1 of 66.7%, whereas _H. cagayanensis_ and _H. lacunosa_ were further separated at PC2 by 29.6% (Figure 1). This suggests the metabolites compositions of the three species are significantly different from one another, but that _H. cagayanensis_ was especially divergent. This might be due to species-specific volatiles that may serve as marker compounds. The metabolites abundance \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**Formula and**} & \multicolumn{2}{c}{**CAS. No**} & \multicolumn{2}{c}{**Compound**} & \multicolumn{3}{c}{**Plant Species/**} \\ \multicolumn{1}{c}{**Chemical Group**} & & & \multicolumn{3}{c}{**Relative Percentage (\%)**} \\ \cline{4-6} \multicolumn{1}{c}{} & & & _H. cagayanensis_ & _H. lacunosa_ & _H. coriacea_ \\ \hline C\({}_{9}\)H\({}_{18}\)O\({}_{2}\) & 000106-27-4 & \begin{tabular}{c} Butyric acid, \\ isopentyl ester \\ \end{tabular} & - & - & - & 0.31 \\ C\({}_{7}\)H\({}_{12}\)O\({}_{2}\) & 013894-62-7 & \begin{tabular}{c} Z-Methyl \\ 3-hexenoate \\ \end{tabular} & - & - & 0.06 \\ C\({}_{9}\)H\({}_{16}\)O\({}_{2}\) & 007785-66-2 & \begin{tabular}{c} Tglic acid n-butyl \\ ester \\ \end{tabular} & - & - & 0.05 \\ C\({}_{10}\)H\({}_{20}\)O\({}_{2}\) & 002349-07-7 & Isobutyric acid, \begin{tabular}{c} hexyl ester \\ \end{tabular} & - & - & 0.4 \\ Benzenoid & & & & & \\ C\({}_{6}\)H\({}_{25}\)CHO & 000100-52-7 & Benzaldehyde & 5.7 & 2.11 & 1.3 \\ C\({}_{11}\)H\({}_{14}\)O\({}_{2}\) & 000103-37-7 & Benzyl butyrate & - & - & 0.31 \\ C\({}_{10}\)H\({}_{12}\)O\({}_{2}\) & 000097-53-0 & p-Eugenol & 7.1 & 2.55 & - \\ C\({}_{8}\)H\({}_{8}\)O\({}_{3}\) & 000119-36-8 & Methyl salicate & 24.67 & 1.75 & 0.66 \\ C\({}_{7}\)H\({}_{8}\)O & 000100-51-6 & Phenylmethanol & 0.36 & - & 2.05 \\ C\({}_{7}\)H\({}_{8}\)O & 000106-44-5 & p-Cresol & 0.13 & - & - \\ Alkenes & & & - & - & - \\ C\({}_{15}\)H\({}_{24}\) & 054274-73-6 & \begin{tabular}{c} Bicycloesquiphe \\ llandrene \\ \end{tabular} & - & - & 0.17 \\ C\({}_{6}\)H\({}_{10}\) & 000693-89-0 & Methylcyclopentene & & - & 0.3 \\ C\({}_{10}\)H\({}_{14}\) & 000460-01-5 & Cosmee & 0.65 & - & \\ C\({}_{7}\)H\({}_{12}\) & 000591-47-9 & Methylcyclohexene & - & - & 0.03 \\ C\({}_{6}\)H\({}_{12}\) & 000625-27-4 & \begin{tabular}{c} 2-Methyl-2- \\ pentene \\ \end{tabular} & 0.48 & - & - \\ Aldehydes & & & & \\ C\({}_{6}\)H\({}_{12}\)O & 000066-25-1 & Hexaldehyde & 1.19 & - & - \\ C\({}_{8}\)H\({}_{8}\)O & 000122-78-1 & Phenylacetaldehyde & - & 2.36 & - \\ C\({}_{9}\)H\({}_{14}\)O & 017587-33-6 & \
\begin{tabular}{c} (E,E)-2,6- \\ Nonadienal \\ \end{tabular} & - & - & 1.73 \\ Ketone & & & & \\ C\({}_{8}\)H\({}_{14}\)O & 010408-15-8 &
\begin{tabular}{c} 6-Methyl-6- \\ hepten-2-one \\ \end{tabular} & - & 4.71 & - \\ C\({}_{13}\)H\({}_{22}\)O & 003796-70-1 & Geranyl acetone & - & 0.42 & - \\ Acid & & & & \\ C\({}_{5}\)H\({}_{8}\)O\({}_{2}\) & 000080-59-1 & Tiglic acid & - & - & 0.94 \\ Sulphur & & & & \\ C\({}_{2}\)H\({}_{6}\)S & 000075-08-1 & Ethanethiol & - & - & 0.11 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._marked the differences between the flowers of all species studied as statistically significant with a \(p\)-value less than 0.05. These are depicted in the heatmap (Figure 2). Figure 1: Principal component analysis (PCA) plot of metabolites from three species of _Hoya_. Each colour in scores plot represents a different species; _H. cagavanensis_ (red), _H. lacunosa_ (green), and _H. coriacea_ (blue). Figure 2: Heat map represents metabolites of different abundance between the flowers of _Hoya_ species. Red hues indicate high metabolite content and blue hues indicate low metabolite content.