The Eugenia and Syzygium genera include approximately 1000 and 1800 species, respectively, and both belong to the Myrtaceae. Their species present economic and medicinal importance and pharmacological properties. Due to their chemical diversity and biological activity, we are reporting the essential oils of 48 species of these two genera, which grow in South America and found mainly in Brazil. Chemically, a total of 127 oil samples have been described and displayed a higher intraspecific and interspecific diversity for both Eugenia spp. and Syzygium spp., according to the site of collection or seasonality. The main volatile compounds were sesquiterpene hydrocarbons and oxygenated sesquiterpenes, mainly with caryophyllane and germacrane skeletons and monoterpenes of mostly the pinane type. The oils presented many biological activities, especially antimicrobial (antifungal and antibacterial), anticholinesterase, anticancer (breast, gastric, melanoma, prostate), antiprotozoal (Leishmania spp.), antioxidant, acaricidal, antinociceptive and anti-inflammatory. These studies can contribute to the rational and economic exploration of Eugenia and Syzygium species once they have been identified as potent natural and alternative sources to the production of new herbal medicines.

Eugenia patrisii Vahl is a native and non-endemic myrtaceous species of the Brazilian Amazon. Due to few botanical and phytochemical reports of this species, the objective of the present work was to evaluate the seasonal variability of their leaf essential oils, performed by GC and GC-MS and chemometric analysis. The results indicated that the variation in oil yields (0.7 ± 0.1%) could be correlated with climatic conditions and rainy (R) and dry seasons (D). (E)-caryophyllene (R = 17.1% ± 16.0, D = 20.2% ± 17.7) and caryophyllene oxide (R = 30.1% ± 18.4, D = 14.1% ± 19.3) are the major constituents and did not display significant differences between the two seasons. However, statistically, a potential correlation between the main constituents of E. patrisii essential oil and the climatic parameters is possible. It was observed that the higher temperature and insolation rates and the lower humidity rate, which are characteristics of the dry season, lead to an increase in the (E)-caryophyllene contents, while lower temperature and insolation and higher humidity, which occur in the rainy season, lead to an increase in the caryophyllene oxide content. The knowledge of variations in the E. patrisii essential oil composition could help choose the best plant chemical profile for medicinal purposes.

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.

Aniba canelilla (Kunth) Mez essential oil has many biological activities due to its main compound 1-nitro-2-phenylethane (1N2F), followed by methyleugenol, a carcinogenic agent. This study analyzed the influence of seasonality on yields, antioxidant capacity, and 1N2F content of A. canelilla leaf and twig essential oils. Essential oils (EOs) were extracted with hydrodistillation and analyzed with gas chromatography coupled to mass spectrometry and a flame ionization detector. Antioxidant capacity was measured using the free radical scavenging method (DPPH). Chemometric analyses were carried out to verify the influence of climatic factors on the production and composition of EOs. 1-Nitro-2-phenylethane was the major constituent in A. canelilla EOs throughout the seasonal period (68.0–89.9%); methyleugenol was not detected. Essential oil yields and the 1N2F average did not show a statistically significant difference between the dry and rainy seasons in leaves and twigs. Moderate and significant correlations between major compounds and climate factor were observed. The twig oils (36.0 ± 5.9%) a showed greater antioxidant capacity than the leaf oils (20.4 ± 5.0%). The PCA and HCA analyses showed no statistical differences between the oil samples from the dry and rainy seasons. The absence of methyleugenolin in all months of study, described for the first time, makes this specimen a reliable source of 1N2F.