## 2 Results  
Cultivar-Specific Volatile Profiles Unveil the Intricate Levels and Blends of Floral Scent in Herbaceous Peony  
Headspace solid-phase microextraction (HS-SPME) in conjunction with gas chromatography-mass spectrometry (GC-MS) analysis identified 95 volatile organic compounds (VOCs) in twenty-four whole flowers from herbaceous peony (Figure 1A, Table S1). After filtering with the criterion that the relative percentage of one component should be no less than 1% in at least 1 of these 24 cultivars, 53 VOCs were divided into different groups (Figure 1B). Notably, terpenoids such as 1,8-cineole, citronellol, geraniol, and \(\beta\)-caryophyllene, as well as phenylpropanol-related compound 2-PE were dominant VOCs detected in most peony flowers. Although phenolic methyl ethers, such as 1,4-dimethoxybenzene, contain a benzene skeleton, they are not derived from aromatic amino acids. Instead, they belong to a specific chemical class that contributes to the scent of certain plant varieties. Moreover, R-(\(-\))-3-hydroxy-\(\beta\)-ionone, a derivative of carotenoids, was grouped together with 1,4-dimethoxybenzene as other VOCs (Figure 1B). Esters formed by terpenoids and fatty acids were tentatively grouped as fatty acid derivatives. Interestingly, the relative contents of the VOCs varied significantly among different peony cultivars. For example, most cultivars' flowers exhibited notably high levels of 2-PE. However, 2-PE was not detected in _P. lactiflora_ cv. Zifengyu, _P. lactiflora_ cv. Zhongshengfen, _P. lactiflora_ cv. Fenfurong, or _P. lactiflora_ cv. Saifugui flowers. Citronellol was dominantly present in _P. lactiflora_ cv. Jarcoma, _P. lactiflora_ cv. Heixiuqiu, and _P. lactiflora_ cv. Zifengyu, while \(\beta\)-caryophyllene was highly detected in _P. lactiflora_ cv. Fenchijinyu and _P. lactiflora_ cv. Fenfurong flowers. Figure 1: Floral VOC emission profiles in herbaceous peony. **(A)** Peony cultivar flowers. The twenty-four cultivar flowers were used to examine volatile emission profiles. **(B)** The contents of floral VOCs released from different herbaceous peony cultivars. Specific relative contents are provided in Table S1. To determine the dominant and divergent scent compounds, the floral volatiles were subjected to principal component analysis (PCA). In detail, 2-PE, 1,4-dimethedoxybenzene, citronellol, geraiol, \(\beta\)-caryophyllene, and 1,8-cineole were identified as the most dominant floral VOCs conferring the aroma diversity to herbaceous peony (Figure 2A). As noted in previous studies [40], terpenoids appear as leading compounds, followed by volatile phenylpropanol-related (C6-C2) compounds, fatty acid derivatives, and other compounds in peony plants (Figure 2B). For instance, terpenoids were highly observed in _P. lactifora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], and _P. lactiflora_ cv. [PERSON]. Comparatively, phenylpropanol-related (C6-C2) compounds were dominantly identified in _P. lactiflora_ cv. [PERSON], _P. lactiflora_ cv. [PERSON], and _P. lactiflora_ cv. [PERSON]. Generally, fatty acid derivatives were found in all peony cultivars under this study, albeit at relatively lower levels compared to other VOCs. In summary, the volatile analysis of twenty-four cultivar flowers showed distinct variations in contents and the complexity of scent blends in _Paeonia_ taxa. Figure 2: PCA and VOC comparison among the twenty-four herbaceous peony cultivars. (**A**) PCA of floral volatiles. The values 39% (x-axis) and 16.9% (y-axis) indicate the contribution rate. (**B**) The contents of benzenoids/phenylpropanoids, terpenoids, and fatty acid derivatives.