## 2 Results and Discussion
### Volatile Compounds of Chrysanthemum and Its Wild Relatives  
Plants produce diverse secondary metabolites, produce and store a wide range of volatile organic compounds in their flowers. The compound identification was based solely on mass spectrometric data comparison. In total, 193 volatile organic compounds were tentative identified by comparison with known libraries (Table S1); this number is greater than that reported in a previous study [30]. Several of the compounds have been identified previously in _Chrysanthemum_[19]. Different species contained different types and quantities of floral volatile compounds. The number of volatile compounds ranged from 10 (in \"Nan nong wu feng che\") to 45 (in \"Nan nong jin kou\"). Among the 39 accessions, 37 accessions had 10-39 types of volatile compounds; 19 accessions had 20-29 types of volatile compounds; and 2 accessions had more than 40 types of volatile compounds (Table 2). The 193 volatile compounds were categorized into four groups; terpen, oxygenated terpen, aromatic compounds, and others. The terpenes group included 39 monoterpencids, 27 sesquiterpenes and 17 irregular terpenoids; together, terpenes accounted for 82 of the 193 compounds. All of the oxygenated terpenes were oxygenated monoterpencids, and included 23 monoterpencoid derivative ketones, 15 monoterenoid derivative alcohols, 11 monoterenoid derivative aldehydes and 11 monoterenoid derivative esters; together, these four types of oxygenated monoterpencids accounted for 60 of the 193 compounds. There were 27 aromatic compounds and 11 other compounds. Figure 1: Representative different flower types of _Chrysanthemum_ and chemical composition of flower headspace volatiles. (**a**) Wild relatives; (**b**) spider type; (**c**) pomon type; (**d**) anemone type; (**e**) single-flower; (**f**) double-flowers. Individual stacked bars reflect the relative composition of flower volatiles by chemical group. These included 13 esters, five alkanes, three alkynes, one olefin, and one nitrogenous compound. Oxygenated terpenes (15.72%-96.53%) and terpenes (2.42%-78.84%) were the major groups of compounds. The contents of these two compounds covered a broad range from 85.55% to 100%, except in _Jiania myriantha_, in which oxygenated terpenes and terpenes accounted for only 41.35% of the total volatile compounds. Oxygenated terpenes and terpenes accounted for at least 95% of the total floral scent volatiles in accessions. Sesquiterpenes accounted for a small percentage (0.00%-4.34%) of total volatiles, except in \"Chu ju\", where they accounted for 25.05% of total volatiles. Aromatic compounds also accounted for small proportions (0%-4.89%) of total volatiles in 36 accessions, but _Ajania myriantha_, \"Hang bai ju\", and _C. indicum_ collected from Huangshan contained higher proportions of aromatic compounds (20.43%, 14.45%, and 11.56%, respectively). The sample of _C. indicum_ collected from different locations also showed large differences in the main volatile compounds. Also, differences among the minor components in each chemical group may further distinguish the accessions from each other. All terpenids and their oxygenated compounds are biosynthesized from the same substrates [31]. The triterpene diols and triols from edible _Chrysanthemum_ flowers have been shown to have anti-tumor activity [32,33]. Therefore, \"Nan nong jin kou\", \"Nan nong ju yu\", \"Yi dian hei\", \"Nan nong huang kou\", \"Nan nong xue rong\", and \"Nan nong fen feng che\", which contained higher proportions of triterpene diols and triols, may be candidate cultivars for tea chrysanthemum (Figure 1). \(\alpha\)-Pinene was present in 36 accessions but absent from \"Nan nong fen feng che\", \"Nan nong ju yu\", and \"Zhe jiang 12\". Its concentration ranged from 0.08 \(\mu\)g g\({}^{-1}\) in \"Chi huang\" to 10.03 \(\mu\)g g\({}^{-1}\) in \"Nan nong xia yu\", with an average content of 1.24 \(\mu\)g g\({}^{-1}\) across the 36 accessions.