ABSTRACT
Allamanda species [Apocynaceae] are popular ornamentals. Additionally, A. cathartica possesses medicinal properties whereas all other species have not been reported. This research aims to analyze genetics and chemical contents of Allamanda species existing in Thailand. The explored species are A. blanchetii, A. cathartica, A. neriifolia, A. schottii, and A. violacea. The dendrogram constructed from 16 inter-simple sequence repeat markers clearly distinguished species with genetic similarity values of 0.92-0.93 for species level and 0.50-0.76 for genus level. Diverse chemicals content in hexane extracts from A. blanchetii, A. neriifolia, A. schottii, and A. violacea were detected by gas chromatography-mass spectrometry. A high amount of squalene was found in A. blanchetii [55.81%] and A. violacea [51.09%]. This content may function as a chemo preventative substance to protect people from cancer. Alpha-Tocopherol, a form of vitamin E, was one of the predominant components found in A. violacea [26.325%], A. schottii [15.41%], and A. neriifolia [9.16%]. One more substance, 9,12,15-octadecatrien-1-ol, was found to be relatively high in A. schottii [17.31%] and A. neriifolia [15.51%]. Other minor and unknown compounds were also detected. The discovery of these chemicals provides an alternative and supplement for improving human well-being and pharmaceutical industries with natural resources, especially in light of the population increase.