Seasonal and Circadian Evaluation of the Essential Oil of Dizygostemon riparius (Plantaginaceae), a Wild Flavoring Herb from East Maranhão, Brazil.

Dizygostemon riparius (Plantaginaceae) is an aromatic herbal species known as "Melosa", endemic to the Municipality of São Benedito do Rio Preto, East Maranhão state, Brazil. It has a refreshing and pleasant aroma and is used for food flavoring and controlling domestic animal parasites. This work aimed to evaluate the seasonal and circadian influence on the composition and production of essential oils (EOs) from D. riparius. The plant aerial parts were hydrodistilled, and the oils were analyzed by GC and GC/MS. The seasonal study was conducted from August 2019 to July 2020, and the circadian study in dry (November) and rainy (May) periods, at 6 am, 12 am, and 6 pm. The results showed that the medium EOs yield was 2.8 %, and the primary constituents (>2 %) were endo-fenchyl acetate (30.5-42.1 %) and endo-fenchol (31.6-37.4 %), (E)-caryophyllene (2.8-7.6 %), α-fenchene (3.3-6.5 %), p-cymene (0.7-4.5 %), and caryophyllene oxide (1.4-2.7 %). Yield and composition of EOs did not significantly correlate with the climatic parameters, but their seasonal percentages influenced their two main components due to precipitation and solar radiation environmental factors. Quantitative variability in the EOs composition during the dry and rainy seasons was observed in the circadian period. These data may be significant for the plant's economic use.