Interspecific variations in the habitats of (L.) Roth leading to changes in its bioactive constituents and allelopathic activity.

is an annual plant growing in different habitats of the Egyptian deserts. Little is known about variation among the habitats occupied by this species, its distribution, chemical composition, and allelopathic activity. The present study aimed to (a) assess the vegetation composition of three different habitats (Western Coast, Delta Coast, and Wadi Hagoul) of in Egypt, (b) determine their correlation to soil factors, (c) identify the changes in the bioactive constituents of in the three regions, and (d) evaluate the allelopathic activity regarding the variation in the habitat. Density and cover of all plant species associated with were estimated within 52 plots, representing three regions. Physical and chemical parameters of soil were analyzed in each plot. aboveground biomass was collected from each habitat, and the bioactive composition was analyzed using HPLC. The allelopathic effect against two weeds ( and ) was assessed. The floristic composition showed the presence of 133 species belonging to 27 families. In the Delta Coast habitat of , and co-dominate, while dominate the Western Coast habitat and finally the habitat of Wadi Hagoul was dominated by . Soil analysis revealed little variations among habitats, especially salinity and organic matter. Fifteen compounds, mainly phenolics (60% of the total identified compounds) were identified from all samples. The major compounds were quercetin, naringenin, ellagic, gallic, chlorogenic, and caffeic acids. These compounds varied in diversity or quantity among different habitats. The Western Coast sample was the richest in species, followed by Delta Coast sample. Our study showed that salinity is the crucial factor that induces the production of bioactive constituents in , especially phenolics and flavonoids. The extracts significantly reduced the germination and growth of and . However, the Western Coast sample showed potent allelopathic activity, where the germination was wholly inhibited at 75 mg L and 50 mg L, respectively. Thereby, this extract could be used as eco-friendly bioherbicide and may be integrated into weed control strategies.