Myrciaria (Myrtaceae) species have been well investigated due to their chemical and biological relevance. The present work aimed to carry out the chemotaxonomic study of essential oils of the species M. dubia, M. floribunda, and M. tenella, sampled in the Brazilian Amazon and compare them with the volatile compositions from other Myrciaria species reported to Brazil and Colombia. The leaves of six Myrciaria specimens were collected (PA, Brazil) during the dry season, and their chemical compositions were analyzed by gas chromatography-mass spectrometer (GC-MS) and gas chromatography-flame ionization detector (GC-FID). The main compounds identified in the essential oils were monoterpenes with pinane and menthane skeletons, followed by sesquiterpenes with caryophyllane and cadinane skeletons. Among the sampled Myrciaria specimens, five chemical profiles were reported for the first time: profile I (M. dubia, α-pinene, 54.0–67.2%); profile II (M. floribunda, terpinolene 23.1%, α-phellandrene 17.7%, and γ-terpinene 8.7%); profile III (M. floribunda, γ-cadinene 17.5%, and an unidentified oxygenated sesquiterpene 15.0%); profile IV (M. tenella, E-caryophyllene 43.2%, and α-humulene 5.3%); and profile V (M. tenella, E-caryophyllene 19.1%, and caryophyllene oxide 41.1%). The Myrciaria chemical profiles showed significant variability in extraction methods, collection sites, plant parts, and genetic aspects.

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Psidium friedrichsthalianum (Myrtaceae) is a small tree with antioxidant activity in its fruits and antimicrobial activity in its leaves and thin branches. The present study analyzed the seasonal variability in the yield and essential oil composition of a P. friedrichsthalianum population in Belém, Brazil. Essential oils were obtained by hydrodistillation and analyzed by gas chromatography (GC) coupled to mass spectrometer (MS) and flame ionization detector (FID). Chemometric analyses were carried out to verify the climatic influence on the production and composition of the essential oil. The average oil yield in the dry season (August–February) was 0.5 ± 0.0%, and in the rainy season (March–May), it was 0.8 ± 0.0%, with statistical differentiation. There was a moderate correlation between oil yield and the collection area’s relative humidity (r = 0.63). The PCA and HCA analyses did not show differentiation between the P. friedrichsthalianum oil samples during the dry and rainy seasons. However, the class of monoterpene hydrocarbons presented a negative correlation with temperature (r = −0.81) and humidity (−0.80) of the sampled area. In the PCA and HCA studies, the samples were classified into three groups: Group I (leaf oils) was characterized by a higher content of α-pinene (6.3–18.0%), β-elemene (9.9–14.8%), caryophyllene oxide (4.3–16.3%), and β-pinene (4.8–13.4%). Group II (leaf oils) was defined by a higher content of selin-11-en-4-α-ol (4.6–15.6%), β-elemene (9.9–14.8%), α-pinene (6.3–18.0%), and E-caryophyllene (3.1–8.7%). Group III (fruits volatile concentrate) was characterized by a higher content of α-pinene (17.6%), α-terpineol (13.7%), and selin-11-en-4-α-ol (10.0%). There was significant seasonal variability in P. friedrichsthalianum, whose responses are directly linked to abiotic factors such as precipitation, insolation, humidity, and temperature.