| Summary: | <i>Pulicaria</i> genus (fleabane) is characterized by its fragrant odor due to the presence of essential oil (EO). According to the literature reviews, the EO of <i>Pulicaria</i> <i>somalensis</i> O.Hoffm. (Shie) is still unexplored. For the first time, 71 compounds were characterized in EO derived from above-ground parts of <i>P. somalensis</i> collected from Saudi Arabia. Sesquiterpenes represented the main components (91.8%), along with minor amounts of mono-, diterpenes, and hydrocarbons. Juniper camphor (24.7%), <i>α</i>-sinensal (7.7%), 6-epi-shyobunol (6.6%), <i>α</i>-zingiberene (5.8%), <i>α</i>-bisabolol (5.3%), and T-muurolol (4.7%) were characterized as main constituents. The correlation analysis between different <i>Pulicaria</i> species showed that <i>P. somalensis</i> has a specific chemical pattern of the EO, thereby no correlation was observed with other reported <i>Pulicaria</i> species. The EO showed significant allelopathic activity against the weeds of <i>Dactyloctenium aegyptium</i> (L.) Willd. (crowfoot grass) and <i>Bidens pilosa</i> L. (hairy beggarticks). The IC<sub>50</sub> value on the germination of <i>D. aegyptium</i> was double that of <i>B. pilosa</i>. The IC<sub>50</sub> values on the root growth of <i>B. pilosa</i> and <i>D. aegyptium</i> were 0.6 mg mL<sup>−1</sup> each, while the shoot growths were 1.0 and 0.7 mg mL<sup>−1</sup>, respectively. This variation in the activity could be attributed to the genetic characteristics of the weeds. Moreover, the EO exhibited significant antioxidant effects compared to ascorbic acid. Further studies are necessary to verify if these biological activities of the EO could be attributable to its major compounds.
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