"Xinyi" (Magnolia biondii Pampan., Magnolia denudata Desr., and Magnolia sprengeri Pampan.) is a traditional Chinese medicine listed in the Pharmacopoeia of the People's Republic of China. "Xinyi" has anti-inflammatory, anti-allergic, antioxidant, and antibacterial effects, and has significant curative effects in the treatment of acute and chronic rhinitis, allergic rhinitis, and other rhinitis symptoms. However, comparative quality assessments of these three species are scarce. This study investigated the variations in the volatile oil content and composition in the flower buds of M. biondii, M. denudata, and M. sprengeri using the gas chromatography-mass spectrometry (GC-MS) and the microscopic analysis at different growth stages. This study indicated the following findings. (1) The volatile oil levels varied among the species, with M. biondii, M. denudata, and M. sprengeri peaking, respectively. In addition, the cell density was positively correlated with the oil deposition. (2) The content of 1,8-Cineole varied significantly, where M. biondii exhibited the high levels at 14.50% at stage 4 and 16.40% at stage 5
M. denudata peaked at 17.87% at stage 5
and M. sprengeri was 1.07% at stage 3. Moreover, M. biondii and M. denudata from Hubei exceeded the Pharmacopoeia's 1% standard, whereas M. sprengeri did not. These findings underscore the need to improve the herb production standards and provide valuable data for assessing the therapeutic potential of these "Xinyi" species.