Comparative Phytochemical Analysis of Five Species of the Genus Arthrophytum Schrenk (Amaranthaceae) from the Flora of Kazakhstan

Background: The genus Arthrophytum Schrenk (Amaranthaceae Juss.) is a relict systematic group restricted to the desert regions of northern Turan. Its species are narrowly endemic, stenotopic, and poorly studied, with virtually no available data on their phytochemical composition. Objectives: This study aimed to conduct the first comparative phytochemical analysis of five Arthrophytum species—A. lehmannianum, A. iliense, A. longibracteatum, A. subulifolium, and A. betpakdalense—to reveal their metabolite profiles and assess chemotaxonomic and functional features. Methods: Phytochemical profiling was performed using gas chromatography–mass spectrometry (GC–MS) to identify volatile and semi-volatile metabolites in the studied species. Results: GC–MS analysis revealed a predominance of terpenes in all species, along with significant contributions from fatty acids, esters, and other oxygen-containing compounds. The taxa were characterized by a rich pool of isoprenoids, including terpenes, sterols, tocopherols, and squalene, as well as lipid components of cuticular coatings such as fatty acids and long-chain alcohols. Isoprenoids dominated particularly in A. subulifolium and A. longibracteatum. A. iliense showed a high content of carbonyl and aromatic compounds, whereas A. longibracteatum and A. lehmannianum were distinguished by elevated levels of fatty acids and long-chain alcohols. Common metabolites—β-sitosterol, stigmasterol, vitamin E, squalene, and caryophyllene—constituted the conservative biochemical core of the genus. Conclusions: The results obtained for the first time demonstrate distinct chemotaxonomic and functional features of relict Arthrophytum species and highlight their potential for further research and application in the pharmaceutical, cosmetic, and aromatic industries.