Chemical characterisation of the essential oils of three <i>Baccharis</i> species: <i>Baccharis pentodonta</i> Malme, <i>Baccharis tridentata</i> Vahl, and <i>Baccharis linearifolia</i> Pers

<i>Baccharis</i> species (Asteraceae) are widely used in South American traditional medicine and produce essential oils rich in bioactive terpenoids. This study investigated the chemical composition of essential oils from leaves and inflorescences of male and female specimens of <i>Baccharis pentodonta</i>, <i>Baccharis linearifolia</i>, and <i>Baccharis tridentata</i>. Essential oils were obtained by hydrodistillation and analysed by GC-MS and NMR spectroscopy (¹H,¹³C, and 2D). The oils of <i>B. pentodonta</i> and <i>B. tridentata</i> showed similar chemical profiles between sexes, dominated by oxygenated sesquiterpenes, particularly spathulenol, α-cadinol, torreyol, and caryophyllene oxide. In contrast, <i>B. linearifolia</i> exhibited marked sexual dimorphism: female specimens were characterised by high proportions of (<i>E</i>)-nerolidol, whereas male specimens accumulated 4,7(11)-amorphadien-8-one, whose structure was confirmed by NMR. These results expand current knowledge on the chemical composition of <i>Baccharis</i> essential oils, highlight the relevance of sexual dimorphism in <i>B. linearifolia</i>, and contribute to the chemotaxonomic understanding of this medicinally important genus.