###### Abstract  
The physical properties, chemical composition, enantiomer distribution, and cholinesterase (ChE) inhibitory activity were determined for a steam-distilled essential oil (EO), with a yield of 0.15 \(\pm\) 0.05 % (_w/w_), from _H. Iarricifolium_ aerial parts, collected in southern Ecuador. The oil qualitative and quantitative analyses were performed by GC-EIMS and GC-FID techniques, using two capillary columns containing a non-polar 5%-phenyl-methylpolysiloxane and a polar polyethylene glycol stationary phase, respectively. The main constituents (>10%) detected on the two columns were, respectively, limone (24.29, 23.16%), (E)-\(\beta\)-cimeime (21.89, 27.15%), and (Z)-\(\beta\)-cimeime (12.88, 16.03%). The EO enantioselective analysis was carried out using a column based on 2,3-diethyl-6-_tert_-butyldimethylsilyl-\(\beta\)-cyclodextrintrin. Two mixtures of chiral monoterenes were detected containing (1,5R)-(+)-\(\alpha\)-pinene (_ce_ = 83.68%), and (S)-(-)-limone (_ce_ = 88.30%) as the major enantiomers. This finding led to some hypotheses about the existence in the plant of two enantioselective biosynthetic pathways. Finally, the EO exhibited selective inhibitory effects in vitro against butylcholinesteraseterase (BuChE) (IC\({}_{50}\) = 36.80 \(\pm\) 2.40 \(\mu\)g/mL), which were about three times greater than against acetylcholinesterase-cholinesterase (IC\({}_{50}\) = 106.10 \(\pm\) 20.20). Thus, the EO from Ecuadorian _H. Iarricifolium_ is an interesting candidate for investigating the mechanism of the selective inhibition of BuChE and for discovering novel drugs to manage the progression of Alzheimer's disease. Hypericum Iarricifolium; essential oil; constituents; enantioselective analysis; AChE and BuChE inhibitory effects 2022112962202211296220221129622022112962202211296220221129622022112962202211296220221129622022112962220221129622202211296222022112962220221129622202221129622202211296222112296222  
claims are still debated. In fact, thanks to some clinical studies and meta-analysis reviews supporting the efficacy, St. John's word may be prescribed in Germany for mild to moderate depression. On the contrary, in the United States, the plant is considered as only a dietary supplement by the FDA and is not regulated by the same standards as a prescription drug. Moreover, in pastures, St John's word acts as an invasive weed and in large doses is poisonous to grazing livestock. Phytochemical studies carried out on different _Hypericum_ taxa have revealed the presence of bioactive specialized metabolites belonging to different classes, including phloroglucinols, napthodianthrones, flavonoids, phenylpropanes, essential oils (EOs), benzophenones, and xanthones [9; 10]. Most compounds show a wide range of biological properties, such as antimicrobial [11; 12; 13], anti-inflammatory [14], anticholinesterase [15; 16], anti-cancer [17; 18], antioxidant [19; 20], anticholinesterase [20], hypoglycemic [21], anti-collagenase and anti-elastase [22], immunosuppressive [23; 24], and immunomododulatory effects [25]. For example, the naphthodianthrones hypericin and pseudohypericin, the prenylated phloroglucinol hyperorin, and the flavonoid amentofavone are considered the main compounds responsible for the antidepressant activity of _H. perforatum_[7; 8; 9]. The _Catalogue of the Vascular Plants of Ecuador_ documents 22 accepted _Hypericum_ species known to occur in Ecuador. Of the total figure, 3 species are introduced and, of the 19 native species, 8 are recorded as endemic to Ecuador [26; 27]. Interestingly, _H. perfora-tum_ is not included in the list. We have focused our interest on _Hypericum laricifolium_ [PERSON]. (Synonyms: _Brathys acer-osa ([PERSON])_ [PERSON], _B. laricifolia_ ([PERSON].) [PERSON]; _Hypericum acerosum_ [PERSON]; _H. laricoides_ [PERSON], et al., _H. laricifolium_ var. _acerosum_ ([PERSON]) [PERSON], _H. platypetatum_ [PERSON], _H. racemulosum_ [PERSON]. [28]).